Merge branch 'main' into use-catch2

1 files changed, 1811 insertions, 426 deletions

diff --git a/zenserver/cache/structuredcachestore.cpp b/zenserver/cache/structuredcachestore.cpp
index 738e4c1fd..da948fd72 100644
--- a/zenserver/cache/structuredcachestore.cpp
+++ b/zenserver/cache/structuredcachestore.cpp
@@ -14,13 +14,13 @@
 #include <zencore/logging.h>
 #include <zencore/scopeguard.h>
 #include <zencore/string.h>
-#include <zencore/testing.h>
-#include <zencore/testutils.h>
 #include <zencore/thread.h>
 #include <zencore/timer.h>
 #include <zencore/trace.h>
 #include <zenstore/cidstore.h>
 
+#include <xxhash.h>
+
 #if ZEN_PLATFORM_WINDOWS
 #	include <zencore/windows.h>
 #endif
@@ -30,10 +30,183 @@ ZEN_THIRD_PARTY_INCLUDES_START
 #include <gsl/gsl-lite.hpp>
 ZEN_THIRD_PARTY_INCLUDES_END
 
+#if ZEN_WITH_TESTS
+#	include <zencore/testing.h>
+#	include <zencore/testutils.h>
+#	include <zencore/workthreadpool.h>
+#	include <random>
+#endif
+
 //////////////////////////////////////////////////////////////////////////
 
 namespace zen {
 
+namespace {
+
+#pragma pack(push)
+#pragma pack(1)
+
+	struct CacheBucketIndexHeader
+	{
+		static constexpr uint32_t ExpectedMagic	 = 0x75696478;	// 'uidx';
+		static constexpr uint32_t CurrentVersion = 1;
+
+		uint32_t Magic			  = ExpectedMagic;
+		uint32_t Version		  = CurrentVersion;
+		uint64_t EntryCount		  = 0;
+		uint64_t LogPosition	  = 0;
+		uint32_t PayloadAlignment = 0;
+		uint32_t Checksum		  = 0;
+
+		static uint32_t ComputeChecksum(const CacheBucketIndexHeader& Header)
+		{
+			return XXH32(&Header.Magic, sizeof(CacheBucketIndexHeader) - sizeof(uint32_t), 0xC0C0'BABA);
+		}
+	};
+
+	static_assert(sizeof(CacheBucketIndexHeader) == 32);
+
+	struct LegacyDiskLocation
+	{
+		inline LegacyDiskLocation() = default;
+
+		inline LegacyDiskLocation(uint64_t Offset, uint64_t ValueSize, uint32_t IndexSize, uint64_t Flags)
+		: OffsetAndFlags(CombineOffsetAndFlags(Offset, Flags))
+		, LowerSize(ValueSize & 0xFFFFffff)
+		, IndexDataSize(IndexSize)
+		{
+		}
+
+		static const uint64_t kOffsetMask = 0x0000'ffFF'ffFF'ffFFull;
+		static const uint64_t kSizeMask	  = 0x00FF'0000'0000'0000ull;  // Most significant bits of value size (lower 32 bits in LowerSize)
+		static const uint64_t kFlagsMask  = 0xff00'0000'0000'0000ull;
+		static const uint64_t kStandaloneFile = 0x8000'0000'0000'0000ull;  // Stored as a separate file
+		static const uint64_t kStructured	  = 0x4000'0000'0000'0000ull;  // Serialized as compact binary
+		static const uint64_t kTombStone	  = 0x2000'0000'0000'0000ull;  // Represents a deleted key/value
+		static const uint64_t kCompressed	  = 0x1000'0000'0000'0000ull;  // Stored in compressed buffer format
+
+		static uint64_t CombineOffsetAndFlags(uint64_t Offset, uint64_t Flags) { return Offset | Flags; }
+
+		inline uint64_t		  Offset() const { return OffsetAndFlags & kOffsetMask; }
+		inline uint64_t		  Size() const { return LowerSize; }
+		inline uint64_t		  IsFlagSet(uint64_t Flag) const { return OffsetAndFlags & Flag; }
+		inline ZenContentType GetContentType() const
+		{
+			ZenContentType ContentType = ZenContentType::kBinary;
+
+			if (IsFlagSet(LegacyDiskLocation::kStructured))
+			{
+				ContentType = ZenContentType::kCbObject;
+			}
+
+			if (IsFlagSet(LegacyDiskLocation::kCompressed))
+			{
+				ContentType = ZenContentType::kCompressedBinary;
+			}
+
+			return ContentType;
+		}
+		inline uint64_t Flags() const { return OffsetAndFlags & kFlagsMask; }
+
+	private:
+		uint64_t OffsetAndFlags = 0;
+		uint32_t LowerSize		= 0;
+		uint32_t IndexDataSize	= 0;
+	};
+
+	struct LegacyDiskIndexEntry
+	{
+		IoHash			   Key;
+		LegacyDiskLocation Location;
+	};
+
+#pragma pack(pop)
+
+	static_assert(sizeof(LegacyDiskIndexEntry) == 36);
+
+	const char* IndexExtension		= ".uidx";
+	const char* LogExtension		= ".slog";
+	const char* LegacyDataExtension = ".sobs";
+
+	std::filesystem::path GetIndexPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
+	{
+		return BucketDir / (BucketName + IndexExtension);
+	}
+
+	std::filesystem::path GetTempIndexPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
+	{
+		return BucketDir / (BucketName + ".tmp" + IndexExtension);
+	}
+
+	std::filesystem::path GetLogPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
+	{
+		return BucketDir / (BucketName + LogExtension);
+	}
+
+	std::filesystem::path GetLegacyLogPath(const std::filesystem::path& BucketDir)
+	{
+		return BucketDir / (std::string("zen") + LogExtension);
+	}
+
+	std::filesystem::path GetLegacyDataPath(const std::filesystem::path& BucketDir)
+	{
+		return BucketDir / (std::string("zen") + LegacyDataExtension);
+	}
+
+	bool ValidateLegacyEntry(const LegacyDiskIndexEntry& Entry, std::string& OutReason)
+	{
+		if (Entry.Key == IoHash::Zero)
+		{
+			OutReason = fmt::format("Invalid hash key {}", Entry.Key.ToHexString());
+			return false;
+		}
+		if (Entry.Location.Flags() & ~(LegacyDiskLocation::kStandaloneFile | LegacyDiskLocation::kStructured |
+									   LegacyDiskLocation::kTombStone | LegacyDiskLocation::kCompressed))
+		{
+			OutReason = fmt::format("Invalid flags {} for entry {}", Entry.Location.Flags(), Entry.Key.ToHexString());
+			return false;
+		}
+		if (!Entry.Location.IsFlagSet(LegacyDiskLocation::kTombStone))
+		{
+			return true;
+		}
+		uint64_t Size = Entry.Location.Size();
+		if (Size == 0)
+		{
+			OutReason = fmt::format("Invalid size {} for entry {}", Size, Entry.Key.ToHexString());
+			return false;
+		}
+		return true;
+	}
+
+	bool ValidateEntry(const DiskIndexEntry& Entry, std::string& OutReason)
+	{
+		if (Entry.Key == IoHash::Zero)
+		{
+			OutReason = fmt::format("Invalid hash key {}", Entry.Key.ToHexString());
+			return false;
+		}
+		if (Entry.Location.GetFlags() &
+			~(DiskLocation::kStandaloneFile | DiskLocation::kStructured | DiskLocation::kTombStone | DiskLocation::kCompressed))
+		{
+			OutReason = fmt::format("Invalid flags {} for entry {}", Entry.Location.GetFlags(), Entry.Key.ToHexString());
+			return false;
+		}
+		if (Entry.Location.IsFlagSet(DiskLocation::kTombStone))
+		{
+			return true;
+		}
+		uint64_t Size = Entry.Location.Size();
+		if (Size == 0)
+		{
+			OutReason = fmt::format("Invalid size {} for entry {}", Size, Entry.Key.ToHexString());
+			return false;
+		}
+		return true;
+	}
+
+}  // namespace
+
 namespace fs = std::filesystem;
 
 static CbObject
@@ -59,7 +232,7 @@ SaveCompactBinaryObject(const fs::path& Path, const CbObject& Object)
 	WriteFile(Path, Object.GetBuffer().AsIoBuffer());
 }
 
-ZenCacheStore::ZenCacheStore(CasGc& Gc, const std::filesystem::path& RootDir)
+ZenCacheNamespace::ZenCacheNamespace(CasGc& Gc, const std::filesystem::path& RootDir)
 : GcStorage(Gc)
 , GcContributor(Gc)
 , m_RootDir(RootDir)
@@ -75,12 +248,12 @@ ZenCacheStore::ZenCacheStore(CasGc& Gc, const std::filesystem::path& RootDir)
 #endif
 }
 
-ZenCacheStore::~ZenCacheStore()
+ZenCacheNamespace::~ZenCacheNamespace()
 {
 }
 
 bool
-ZenCacheStore::Get(std::string_view InBucket, const IoHash& HashKey, ZenCacheValue& OutValue)
+ZenCacheNamespace::Get(std::string_view InBucket, const IoHash& HashKey, ZenCacheValue& OutValue)
 {
 	ZEN_TRACE_CPU("Z$::Get");
 
@@ -118,7 +291,7 @@ ZenCacheStore::Get(std::string_view InBucket, const IoHash& HashKey, ZenCacheVal
 }
 
 void
-ZenCacheStore::Put(std::string_view InBucket, const IoHash& HashKey, const ZenCacheValue& Value)
+ZenCacheNamespace::Put(std::string_view InBucket, const IoHash& HashKey, const ZenCacheValue& Value)
 {
 	ZEN_TRACE_CPU("Z$::Put");
 
@@ -154,7 +327,7 @@ ZenCacheStore::Put(std::string_view InBucket, const IoHash& HashKey, const ZenCa
 }
 
 bool
-ZenCacheStore::DropBucket(std::string_view Bucket)
+ZenCacheNamespace::DropBucket(std::string_view Bucket)
 {
 	ZEN_INFO("dropping bucket '{}'", Bucket);
 
@@ -170,13 +343,13 @@ ZenCacheStore::DropBucket(std::string_view Bucket)
 }
 
 void
-ZenCacheStore::Flush()
+ZenCacheNamespace::Flush()
 {
 	m_DiskLayer.Flush();
 }
 
 void
-ZenCacheStore::Scrub(ScrubContext& Ctx)
+ZenCacheNamespace::Scrub(ScrubContext& Ctx)
 {
 	if (m_LastScrubTime == Ctx.ScrubTimestamp())
 	{
@@ -190,11 +363,11 @@ ZenCacheStore::Scrub(ScrubContext& Ctx)
 }
 
 void
-ZenCacheStore::GatherReferences(GcContext& GcCtx)
+ZenCacheNamespace::GatherReferences(GcContext& GcCtx)
 {
 	Stopwatch  Timer;
-	const auto Guard = MakeGuard(
-		[this, &Timer] { ZEN_INFO("cache gathered all references from '{}' in {}", m_RootDir, NiceTimeSpanMs(Timer.GetElapsedTimeMs())); });
+	const auto Guard =
+		MakeGuard([&] { ZEN_INFO("cache gathered all references from '{}' in {}", m_RootDir, NiceTimeSpanMs(Timer.GetElapsedTimeMs())); });
 
 	access_tracking::AccessTimes AccessTimes;
 	m_MemLayer.GatherAccessTimes(AccessTimes);
@@ -204,14 +377,14 @@ ZenCacheStore::GatherReferences(GcContext& GcCtx)
 }
 
 void
-ZenCacheStore::CollectGarbage(GcContext& GcCtx)
+ZenCacheNamespace::CollectGarbage(GcContext& GcCtx)
 {
 	m_MemLayer.Reset();
 	m_DiskLayer.CollectGarbage(GcCtx);
 }
 
 GcStorageSize
-ZenCacheStore::StorageSize() const
+ZenCacheNamespace::StorageSize() const
 {
 	return {.DiskSize = m_DiskLayer.TotalSize(), .MemorySize = m_MemLayer.TotalSize()};
 }
@@ -425,6 +598,8 @@ ZenCacheDiskLayer::CacheBucket::OpenOrCreate(std::filesystem::path BucketDir, bo
 {
 	using namespace std::literals;
 
+	m_BlocksBasePath = BucketDir / "blocks";
+
 	CreateDirectories(BucketDir);
 
 	std::filesystem::path ManifestPath{BucketDir / "zen_manifest"};
@@ -470,48 +645,465 @@ ZenCacheDiskLayer::CacheBucket::OpenOrCreate(std::filesystem::path BucketDir, bo
 }
 
 void
-ZenCacheDiskLayer::CacheBucket::OpenLog(const fs::path& BucketDir, const bool IsNew)
+ZenCacheDiskLayer::CacheBucket::MakeIndexSnapshot()
 {
-	m_BucketDir = BucketDir;
+	ZEN_INFO("write store snapshot for '{}'", m_BucketDir / m_BucketName);
+	uint64_t   EntryCount = 0;
+	Stopwatch  Timer;
+	const auto _ = MakeGuard([&] {
+		ZEN_INFO("wrote store snapshot for '{}' containing #{} entries in {}",
+				 m_BucketDir / m_BucketName,
+				 EntryCount,
+				 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
+	});
 
-	uint64_t MaxFileOffset	   = 0;
-	uint64_t InvalidEntryCount = 0;
-	m_SobsCursor			   = 0;
-	m_TotalSize				   = 0;
+	namespace fs = std::filesystem;
 
-	m_Index.clear();
+	fs::path IndexPath	   = GetIndexPath(m_BucketDir, m_BucketName);
+	fs::path STmpIndexPath = GetTempIndexPath(m_BucketDir, m_BucketName);
+
+	// Move index away, we keep it if something goes wrong
+	if (fs::is_regular_file(STmpIndexPath))
+	{
+		fs::remove(STmpIndexPath);
+	}
+	if (fs::is_regular_file(IndexPath))
+	{
+		fs::rename(IndexPath, STmpIndexPath);
+	}
+
+	try
+	{
+		m_SlogFile.Flush();
 
-	std::filesystem::path SobsPath{BucketDir / "zen.sobs"};
-	std::filesystem::path SlogPath{BucketDir / "zen.slog"};
+		// Write the current state of the location map to a new index state
+		uint64_t					LogCount = 0;
+		std::vector<DiskIndexEntry> Entries;
 
-	m_SobsFile.Open(SobsPath, IsNew ? BasicFile::Mode::kTruncate : BasicFile::Mode::kWrite);
-	m_SlogFile.Open(SlogPath, IsNew ? CasLogFile::Mode::kTruncate : CasLogFile::Mode::kWrite);
+		{
+			Entries.resize(m_Index.size());
 
-	m_SlogFile.Replay(
-		[&](const DiskIndexEntry& Entry) {
-			if (Entry.Key == IoHash::Zero)
+			uint64_t EntryIndex = 0;
+			for (auto& Entry : m_Index)
 			{
-				++InvalidEntryCount;
+				DiskIndexEntry& IndexEntry = Entries[EntryIndex++];
+				IndexEntry.Key			   = Entry.first;
+				IndexEntry.Location		   = Entry.second.Location;
 			}
-			else if (Entry.Location.IsFlagSet(DiskLocation::kTombStone))
+
+			LogCount = m_SlogFile.GetLogCount();
+		}
+
+		BasicFile ObjectIndexFile;
+		ObjectIndexFile.Open(IndexPath, BasicFile::Mode::kTruncate);
+		CacheBucketIndexHeader Header = {.EntryCount	   = Entries.size(),
+										 .LogPosition	   = LogCount,
+										 .PayloadAlignment = gsl::narrow<uint32_t>(m_PayloadAlignment)};
+
+		Header.Checksum = CacheBucketIndexHeader::ComputeChecksum(Header);
+
+		ObjectIndexFile.Write(&Header, sizeof(CacheBucketIndexHeader), 0);
+		ObjectIndexFile.Write(Entries.data(), Entries.size() * sizeof(DiskIndexEntry), sizeof(CacheBucketIndexHeader));
+		ObjectIndexFile.Flush();
+		ObjectIndexFile.Close();
+		EntryCount = Entries.size();
+	}
+	catch (std::exception& Err)
+	{
+		ZEN_ERROR("snapshot FAILED, reason: '{}'", Err.what());
+
+		// Restore any previous snapshot
+
+		if (fs::is_regular_file(STmpIndexPath))
+		{
+			fs::remove(IndexPath);
+			fs::rename(STmpIndexPath, IndexPath);
+		}
+	}
+	if (fs::is_regular_file(STmpIndexPath))
+	{
+		fs::remove(STmpIndexPath);
+	}
+}
+
+uint64_t
+ZenCacheDiskLayer::CacheBucket::ReadIndexFile()
+{
+	std::vector<DiskIndexEntry> Entries;
+	std::filesystem::path		IndexPath = GetIndexPath(m_BucketDir, m_BucketName);
+	if (std::filesystem::is_regular_file(IndexPath))
+	{
+		Stopwatch  Timer;
+		const auto _ = MakeGuard([&] {
+			ZEN_INFO("read store '{}' index containing #{} entries in {}",
+					 m_BucketDir / m_BucketName,
+					 Entries.size(),
+					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
+		});
+
+		BasicFile ObjectIndexFile;
+		ObjectIndexFile.Open(IndexPath, BasicFile::Mode::kRead);
+		uint64_t Size = ObjectIndexFile.FileSize();
+		if (Size >= sizeof(CacheBucketIndexHeader))
+		{
+			uint64_t			   ExpectedEntryCount = (Size - sizeof(sizeof(CacheBucketIndexHeader))) / sizeof(DiskIndexEntry);
+			CacheBucketIndexHeader Header;
+			ObjectIndexFile.Read(&Header, sizeof(Header), 0);
+			if ((Header.Magic == CacheBucketIndexHeader::ExpectedMagic) && (Header.Version == CacheBucketIndexHeader::CurrentVersion) &&
+				(Header.Checksum == CacheBucketIndexHeader::ComputeChecksum(Header)) && (Header.PayloadAlignment > 0) &&
+				(Header.EntryCount <= ExpectedEntryCount))
 			{
-				m_TotalSize.fetch_sub(Entry.Location.Size(), std::memory_order::relaxed);
+				Entries.resize(Header.EntryCount);
+				ObjectIndexFile.Read(Entries.data(), Header.EntryCount * sizeof(DiskIndexEntry), sizeof(CacheBucketIndexHeader));
+				m_PayloadAlignment = Header.PayloadAlignment;
+
+				std::string InvalidEntryReason;
+				for (const DiskIndexEntry& Entry : Entries)
+				{
+					if (!ValidateEntry(Entry, InvalidEntryReason))
+					{
+						ZEN_WARN("skipping invalid entry in '{}', reason: '{}'", IndexPath, InvalidEntryReason);
+						continue;
+					}
+					m_Index.insert_or_assign(Entry.Key, IndexEntry(Entry.Location, GcClock::TickCount()));
+				}
+
+				return Header.LogPosition;
 			}
 			else
 			{
-				m_Index.insert_or_assign(Entry.Key, IndexEntry(Entry.Location, GcClock::TickCount()));
-				m_TotalSize.fetch_add(Entry.Location.Size(), std::memory_order::relaxed);
+				ZEN_WARN("skipping invalid index file '{}'", IndexPath);
 			}
-			MaxFileOffset = std::max<uint64_t>(MaxFileOffset, Entry.Location.Offset() + Entry.Location.Size());
-		},
-		0);
+		}
+	}
+	return 0;
+}
 
+uint64_t
+ZenCacheDiskLayer::CacheBucket::ReadLog(uint64_t SkipEntryCount)
+{
+	std::vector<DiskIndexEntry> Entries;
+	std::filesystem::path		LogPath = GetLogPath(m_BucketDir, m_BucketName);
+	if (std::filesystem::is_regular_file(LogPath))
+	{
+		Stopwatch					Timer;
+		const auto					_ = MakeGuard([&] {
+			 ZEN_INFO("read store '{}' log containing #{} entries in {}", LogPath, Entries.size(), NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
+		 });
+		TCasLogFile<DiskIndexEntry> CasLog;
+		CasLog.Open(LogPath, CasLogFile::Mode::kRead);
+		if (CasLog.Initialize())
+		{
+			uint64_t EntryCount = CasLog.GetLogCount();
+			if (EntryCount < SkipEntryCount)
+			{
+				ZEN_WARN("reading full log at '{}', reason: Log position from index snapshot is out of range", LogPath);
+				SkipEntryCount = 0;
+			}
+			uint64_t ReadCount = EntryCount - SkipEntryCount;
+			m_Index.reserve(ReadCount);
+			uint64_t InvalidEntryCount = 0;
+			CasLog.Replay(
+				[&](const DiskIndexEntry& Record) {
+					std::string InvalidEntryReason;
+					if (Record.Location.Flags & DiskLocation::kTombStone)
+					{
+						m_Index.erase(Record.Key);
+						return;
+					}
+					if (!ValidateEntry(Record, InvalidEntryReason))
+					{
+						ZEN_WARN("skipping invalid entry in '{}', reason: '{}'", LogPath, InvalidEntryReason);
+						++InvalidEntryCount;
+						return;
+					}
+					m_Index.insert_or_assign(Record.Key, IndexEntry(Record.Location, GcClock::TickCount()));
+				},
+				SkipEntryCount);
+			if (InvalidEntryCount)
+			{
+				ZEN_WARN("found #{} invalid entries in '{}'", InvalidEntryCount, m_BucketDir / m_BucketName);
+			}
+		}
+	}
+	return 0;
+};
+
+uint64_t
+ZenCacheDiskLayer::CacheBucket::MigrateLegacyData(bool CleanSource)
+{
+	std::filesystem::path LegacyLogPath = GetLegacyLogPath(m_BucketDir);
+
+	if (!std::filesystem::is_regular_file(LegacyLogPath) || std::filesystem::file_size(LegacyLogPath) == 0)
+	{
+		return 0;
+	}
+
+	ZEN_INFO("migrating store {}", m_BucketDir / m_BucketName);
+
+	std::filesystem::path LegacyDataPath = GetLegacyDataPath(m_BucketDir);
+
+	uint64_t   MigratedChunkCount = 0;
+	uint32_t   MigratedBlockCount = 0;
+	Stopwatch  MigrationTimer;
+	uint64_t   TotalSize = 0;
+	const auto _		 = MakeGuard([&] {
+		ZEN_INFO("migrated store '{}' to #{} chunks in #{} blocks in {} ({})",
+				 m_BucketDir / m_BucketName,
+				 MigratedChunkCount,
+				 MigratedBlockCount,
+				 NiceTimeSpanMs(MigrationTimer.GetElapsedTimeMs()),
+				 NiceBytes(TotalSize));
+	});
+
+	uint64_t BlockFileSize = 0;
+	{
+		BasicFile BlockFile;
+		BlockFile.Open(LegacyDataPath, CleanSource ? BasicFile::Mode::kWrite : BasicFile::Mode::kRead);
+		BlockFileSize = BlockFile.FileSize();
+	}
+
+	std::unordered_map<IoHash, LegacyDiskIndexEntry, IoHash::Hasher> LegacyDiskIndex;
+	uint64_t														 InvalidEntryCount = 0;
+
+	size_t							  BlockChunkCount = 0;
+	TCasLogFile<LegacyDiskIndexEntry> LegacyCasLog;
+	LegacyCasLog.Open(LegacyLogPath, CleanSource ? CasLogFile::Mode::kWrite : CasLogFile::Mode::kRead);
+	{
+		Stopwatch  Timer;
+		const auto __ = MakeGuard([&] {
+			ZEN_INFO("read store '{}' legacy log containing #{} entries in {}",
+					 LegacyLogPath,
+					 LegacyDiskIndex.size(),
+					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
+		});
+		if (LegacyCasLog.Initialize())
+		{
+			LegacyDiskIndex.reserve(LegacyCasLog.GetLogCount());
+			LegacyCasLog.Replay(
+				[&](const LegacyDiskIndexEntry& Record) {
+					if (Record.Location.IsFlagSet(LegacyDiskLocation::kTombStone))
+					{
+						LegacyDiskIndex.erase(Record.Key);
+						return;
+					}
+					std::string InvalidEntryReason;
+					if (!ValidateLegacyEntry(Record, InvalidEntryReason))
+					{
+						ZEN_WARN("skipping invalid entry in '{}', reason: '{}'", LegacyLogPath, InvalidEntryReason);
+						++InvalidEntryCount;
+						return;
+					}
+					if (m_Index.contains(Record.Key))
+					{
+						return;
+					}
+					LegacyDiskIndex[Record.Key] = Record;
+				},
+				0);
+
+			std::vector<IoHash> BadEntries;
+			for (const auto& Entry : LegacyDiskIndex)
+			{
+				const LegacyDiskIndexEntry& Record(Entry.second);
+				if (Record.Location.IsFlagSet(LegacyDiskLocation::kStandaloneFile))
+				{
+					continue;
+				}
+				if (Record.Location.Offset() + Record.Location.Size() <= BlockFileSize)
+				{
+					BlockChunkCount++;
+					continue;
+				}
+				ZEN_WARN("skipping invalid entry in '{}', reason: location is outside of file", LegacyLogPath);
+				BadEntries.push_back(Entry.first);
+			}
+			for (const IoHash& BadHash : BadEntries)
+			{
+				LegacyDiskIndex.erase(BadHash);
+			}
+			InvalidEntryCount += BadEntries.size();
+		}
+	}
 	if (InvalidEntryCount)
 	{
-		ZEN_WARN("found {} invalid entries in '{}'", InvalidEntryCount, SlogPath);
+		ZEN_WARN("found #{} invalid entries in '{}'", InvalidEntryCount, m_BucketDir / m_BucketName);
 	}
 
-	m_SobsCursor = (MaxFileOffset + 15) & ~15;
+	if (LegacyDiskIndex.empty())
+	{
+		LegacyCasLog.Close();
+		if (CleanSource)
+		{
+			// Older versions of ZenCacheDiskLayer expects the legacy files to exist if it can find
+			// a manifest and crashes on startup if they don't.
+			// In order to not break startup when switching back an older version, lets just reset
+			// the legacy data files to zero length.
+
+			BasicFile LegacyLog;
+			LegacyLog.Open(LegacyLogPath, BasicFile::Mode::kTruncate);
+			BasicFile LegacySobs;
+			LegacySobs.Open(LegacyDataPath, BasicFile::Mode::kTruncate);
+		}
+		return 0;
+	}
+
+	std::filesystem::path LogPath = GetLogPath(m_BucketDir, m_BucketName);
+	CreateDirectories(LogPath.parent_path());
+	TCasLogFile<DiskIndexEntry> CasLog;
+	CasLog.Open(LogPath, CasLogFile::Mode::kWrite);
+
+	std::unordered_map<size_t, IoHash> ChunkIndexToChunkHash;
+	std::vector<BlockStoreLocation>	   ChunkLocations;
+	ChunkIndexToChunkHash.reserve(BlockChunkCount);
+	ChunkLocations.reserve(BlockChunkCount);
+
+	std::vector<DiskIndexEntry> LogEntries;
+	LogEntries.reserve(LegacyDiskIndex.size() - BlockChunkCount);
+
+	for (const auto& Entry : LegacyDiskIndex)
+	{
+		const IoHash&			  ChunkHash = Entry.first;
+		const LegacyDiskLocation& Location	= Entry.second.Location;
+		if (Location.IsFlagSet(LegacyDiskLocation::kStandaloneFile))
+		{
+			uint8_t		 Flags		 = 0xff & (Location.Flags() >> 56);
+			DiskLocation NewLocation = DiskLocation(Location.Size(), Flags);
+			LogEntries.push_back({.Key = Entry.second.Key, .Location = NewLocation});
+			continue;
+		}
+		size_t ChunkIndex = ChunkLocations.size();
+		ChunkLocations.push_back({.BlockIndex = 0, .Offset = Location.Offset(), .Size = Location.Size()});
+		ChunkIndexToChunkHash[ChunkIndex] = ChunkHash;
+		TotalSize += Location.Size();
+	}
+	for (const DiskIndexEntry& Entry : LogEntries)
+	{
+		m_Index.insert_or_assign(Entry.Key, IndexEntry(Entry.Location, GcClock::TickCount()));
+	}
+	CasLog.Append(LogEntries);
+
+	m_BlockStore.Split(
+		ChunkLocations,
+		LegacyDataPath,
+		m_BlocksBasePath,
+		MaxBlockSize,
+		BlockStoreDiskLocation::MaxBlockIndex + 1,
+		m_PayloadAlignment,
+		CleanSource,
+		[this, &LegacyDiskIndex, &ChunkIndexToChunkHash, &LegacyCasLog, &CasLog, CleanSource, &MigratedBlockCount, &MigratedChunkCount](
+			const BlockStore::MovedChunksArray& MovedChunks) {
+			std::vector<DiskIndexEntry> LogEntries;
+			LogEntries.reserve(MovedChunks.size());
+			for (const auto& Entry : MovedChunks)
+			{
+				size_t						ChunkIndex	= Entry.first;
+				const BlockStoreLocation&	NewLocation = Entry.second;
+				const IoHash&				ChunkHash	= ChunkIndexToChunkHash[ChunkIndex];
+				const LegacyDiskIndexEntry& OldEntry	= LegacyDiskIndex[ChunkHash];
+				const LegacyDiskLocation&	OldLocation = OldEntry.Location;
+				uint8_t						Flags		= 0xff & (OldLocation.Flags() >> 56);
+				LogEntries.push_back({.Key = ChunkHash, .Location = DiskLocation(NewLocation, m_PayloadAlignment, Flags)});
+			}
+			for (const DiskIndexEntry& Entry : LogEntries)
+			{
+				m_Index.insert_or_assign(Entry.Key, IndexEntry(Entry.Location, GcClock::TickCount()));
+			}
+			CasLog.Append(LogEntries);
+			CasLog.Flush();
+			if (CleanSource)
+			{
+				std::vector<LegacyDiskIndexEntry> LegacyLogEntries;
+				LegacyLogEntries.reserve(MovedChunks.size());
+				for (const auto& Entry : MovedChunks)
+				{
+					size_t						ChunkIndex	= Entry.first;
+					const IoHash&				ChunkHash	= ChunkIndexToChunkHash[ChunkIndex];
+					const LegacyDiskIndexEntry& OldEntry	= LegacyDiskIndex[ChunkHash];
+					const LegacyDiskLocation&	OldLocation = OldEntry.Location;
+					LegacyDiskLocation			NewLocation(OldLocation.Offset(),
+													OldLocation.Size(),
+													0,
+													OldLocation.Flags() | LegacyDiskLocation::kTombStone);
+					LegacyLogEntries.push_back(LegacyDiskIndexEntry{.Key = ChunkHash, .Location = NewLocation});
+				}
+				LegacyCasLog.Append(LegacyLogEntries);
+				LegacyCasLog.Flush();
+			}
+			MigratedBlockCount++;
+			MigratedChunkCount += MovedChunks.size();
+		});
+
+	LegacyCasLog.Close();
+	CasLog.Close();
+
+	if (CleanSource)
+	{
+		// Older versions of ZenCacheDiskLayer expects the legacy files to exist if it can find
+		// a manifest and crashes on startup if they don't.
+		// In order to not break startup when switching back an older version, lets just reset
+		// the legacy data files to zero length.
+
+		BasicFile LegacyLog;
+		LegacyLog.Open(LegacyLogPath, BasicFile::Mode::kTruncate);
+		BasicFile LegacySobs;
+		LegacySobs.Open(LegacyDataPath, BasicFile::Mode::kTruncate);
+	}
+	return MigratedChunkCount;
+}
+
+void
+ZenCacheDiskLayer::CacheBucket::OpenLog(const fs::path& BucketDir, const bool IsNew)
+{
+	m_BucketDir = BucketDir;
+
+	m_TotalSize = 0;
+
+	m_Index.clear();
+
+	std::filesystem::path LegacyLogPath = GetLegacyLogPath(m_BucketDir);
+	std::filesystem::path LogPath		= GetLogPath(m_BucketDir, m_BucketName);
+	std::filesystem::path IndexPath		= GetIndexPath(m_BucketDir, m_BucketName);
+
+	if (IsNew)
+	{
+		std::filesystem::path LegacyDataPath = GetLegacyDataPath(m_BucketDir);
+		fs::remove(LegacyLogPath);
+		fs::remove(LegacyDataPath);
+		fs::remove(LogPath);
+		fs::remove(IndexPath);
+		fs::remove_all(m_BlocksBasePath);
+	}
+
+	uint64_t LogPosition		 = ReadIndexFile();
+	uint64_t LogEntryCount		 = ReadLog(LogPosition);
+	uint64_t LegacyLogEntryCount = MigrateLegacyData(true);
+
+	CreateDirectories(m_BucketDir);
+
+	m_SlogFile.Open(LogPath, CasLogFile::Mode::kWrite);
+
+	std::vector<BlockStoreLocation> KnownLocations;
+	KnownLocations.reserve(m_Index.size());
+	for (const auto& Entry : m_Index)
+	{
+		const DiskLocation& Location = Entry.second.Location;
+		m_TotalSize.fetch_add(Location.Size(), std::memory_order::relaxed);
+		if (Location.IsFlagSet(DiskLocation::kStandaloneFile))
+		{
+			continue;
+		}
+		const BlockStoreLocation& BlockLocation = Location.GetBlockLocation(m_PayloadAlignment);
+		KnownLocations.push_back(BlockLocation);
+	}
+
+	m_BlockStore.Initialize(m_BlocksBasePath, MaxBlockSize, BlockStoreDiskLocation::MaxBlockIndex + 1, KnownLocations);
+
+	if (IsNew || ((LogEntryCount + LegacyLogEntryCount) > 0))
+	{
+		MakeIndexSnapshot();
+	}
+	// TODO: should validate integrity of container files here
 }
 
 void
@@ -532,12 +1124,13 @@ ZenCacheDiskLayer::CacheBucket::BuildPath(PathBuilderBase& Path, const IoHash& H
 bool
 ZenCacheDiskLayer::CacheBucket::GetInlineCacheValue(const DiskLocation& Loc, ZenCacheValue& OutValue)
 {
-	if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
+	BlockStoreLocation Location = Loc.GetBlockLocation(m_PayloadAlignment);
+
+	OutValue.Value = m_BlockStore.TryGetChunk(Location);
+	if (!OutValue.Value)
 	{
 		return false;
 	}
-
-	OutValue.Value = IoBufferBuilder::MakeFromFileHandle(m_SobsFile.Handle(), Loc.Offset(), Loc.Size());
 	OutValue.Value.SetContentType(Loc.GetContentType());
 
 	return true;
@@ -562,23 +1155,6 @@ ZenCacheDiskLayer::CacheBucket::GetStandaloneCacheValue(const DiskLocation& Loc,
 	return false;
 }
 
-void
-ZenCacheDiskLayer::CacheBucket::DeleteStandaloneCacheValue(const DiskLocation& Loc,
-														   const IoHash&	   HashKey,
-														   const fs::path&	   Path,
-														   std::error_code&	   Ec)
-{
-	ZEN_DEBUG("deleting standalone cache file '{}'", Path);
-	fs::remove(Path, Ec);
-
-	if (!Ec)
-	{
-		m_SlogFile.Append(DiskIndexEntry{.Key = HashKey, .Location = {0, Loc.Size(), 0, DiskLocation::kTombStone}});
-		m_Index.erase(HashKey);
-		m_TotalSize.fetch_sub(Loc.Size(), std::memory_order::relaxed);
-	}
-}
-
 bool
 ZenCacheDiskLayer::CacheBucket::Get(const IoHash& HashKey, ZenCacheValue& OutValue)
 {
@@ -588,23 +1164,21 @@ ZenCacheDiskLayer::CacheBucket::Get(const IoHash& HashKey, ZenCacheValue& OutVal
 	}
 
 	RwLock::SharedLockScope _(m_IndexLock);
-
-	if (auto It = m_Index.find(HashKey); It != m_Index.end())
+	auto					It = m_Index.find(HashKey);
+	if (It == m_Index.end())
 	{
-		IndexEntry& Entry = It.value();
-		Entry.LastAccess.store(GcClock::TickCount(), std::memory_order_relaxed);
-
-		if (GetInlineCacheValue(Entry.Location, OutValue))
-		{
-			return true;
-		}
-
+		return false;
+	}
+	IndexEntry& Entry = It.value();
+	Entry.LastAccess.store(GcClock::TickCount(), std::memory_order_relaxed);
+	DiskLocation Location = Entry.Location;
+	if (Location.IsFlagSet(DiskLocation::kStandaloneFile))
+	{
+		// We don't need to hold the index lock when we read a standalone file
 		_.ReleaseNow();
-
-		return GetStandaloneCacheValue(Entry.Location, HashKey, OutValue);
+		return GetStandaloneCacheValue(Location, HashKey, OutValue);
 	}
-
-	return false;
+	return GetInlineCacheValue(Location, OutValue);
 }
 
 void
@@ -619,54 +1193,13 @@ ZenCacheDiskLayer::CacheBucket::Put(const IoHash& HashKey, const ZenCacheValue&
 	{
 		return PutStandaloneCacheValue(HashKey, Value);
 	}
-	else
-	{
-		// Small object put
-
-		uint64_t EntryFlags = 0;
-
-		if (Value.Value.GetContentType() == ZenContentType::kCbObject)
-		{
-			EntryFlags |= DiskLocation::kStructured;
-		}
-		else if (Value.Value.GetContentType() == ZenContentType::kCompressedBinary)
-		{
-			EntryFlags |= DiskLocation::kCompressed;
-		}
-
-		RwLock::ExclusiveLockScope _(m_IndexLock);
-
-		DiskLocation Loc(m_SobsCursor, Value.Value.Size(), 0, EntryFlags);
-
-		m_SobsCursor = RoundUp(m_SobsCursor + Loc.Size(), 16);
-
-		if (auto It = m_Index.find(HashKey); It == m_Index.end())
-		{
-			// Previously unknown object
-			m_Index.insert({HashKey, {Loc, GcClock::TickCount()}});
-		}
-		else
-		{
-			// TODO: should check if write is idempotent and bail out if it is?
-			// this would requiring comparing contents on disk unless we add a
-			// content hash to the index entry
-			IndexEntry& Entry = It.value();
-			Entry.Location	  = Loc;
-			Entry.LastAccess.store(GcClock::TickCount(), std::memory_order_relaxed);
-		}
-
-		m_SlogFile.Append({.Key = HashKey, .Location = Loc});
-		m_SobsFile.Write(Value.Value.Data(), Loc.Size(), Loc.Offset());
-		m_TotalSize.fetch_add(Loc.Size(), std::memory_order::relaxed);
-	}
+	PutInlineCacheValue(HashKey, Value);
 }
 
 void
 ZenCacheDiskLayer::CacheBucket::Drop()
 {
-	// TODO: add error handling
-
-	m_SobsFile.Close();
+	m_BlockStore.Close();
 	m_SlogFile.Close();
 	DeleteDirectories(m_BucketDir);
 }
@@ -674,11 +1207,10 @@ ZenCacheDiskLayer::CacheBucket::Drop()
 void
 ZenCacheDiskLayer::CacheBucket::Flush()
 {
-	RwLock::SharedLockScope _(m_IndexLock);
-
-	m_SobsFile.Flush();
-	m_SlogFile.Flush();
+	m_BlockStore.Flush();
 
+	RwLock::SharedLockScope _(m_IndexLock);
+	MakeIndexSnapshot();
 	SaveManifest();
 }
 
@@ -724,20 +1256,22 @@ ZenCacheDiskLayer::CacheBucket::Scrub(ScrubContext& Ctx)
 
 			ZenCacheValue Value;
 
-			if (GetInlineCacheValue(Loc, Value))
+			if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
 			{
-				// Validate contents
+				if (GetStandaloneCacheValue(Loc, HashKey, Value))
+				{
+					// Note: we cannot currently validate contents since we don't
+					// have a content hash!
+					continue;
+				}
 			}
-			else if (GetStandaloneCacheValue(Loc, HashKey, Value))
+			else if (GetInlineCacheValue(Loc, Value))
 			{
-				// Note: we cannot currently validate contents since we don't
-				// have a content hash!
-			}
-			else
-			{
-				// Value not found
-				BadKeys.push_back(HashKey);
+				// Validate contents
+				continue;
 			}
+			// Value not found
+			BadKeys.push_back(HashKey);
 		}
 	}
 
@@ -754,12 +1288,18 @@ ZenCacheDiskLayer::CacheBucket::Scrub(ScrubContext& Ctx)
 		{
 			// Log a tombstone and delete the in-memory index for the bad entry
 
-			const auto			It		 = m_Index.find(BadKey);
-			const DiskLocation& Location = It->second.Location;
-			m_SlogFile.Append(DiskIndexEntry{.Key = BadKey, .Location = {Location.Offset(), Location.Size(), 0, DiskLocation::kTombStone}});
+			const auto	 It		  = m_Index.find(BadKey);
+			DiskLocation Location = It->second.Location;
+			Location.Flags |= DiskLocation::kTombStone;
+			m_SlogFile.Append(DiskIndexEntry{.Key = BadKey, .Location = Location});
 			m_Index.erase(BadKey);
 		}
 	}
+
+	// Let whomever it concerns know about the bad chunks. This could
+	// be used to invalidate higher level data structures more efficiently
+	// than a full validation pass might be able to do
+	Ctx.ReportBadCasChunks(BadKeys);
 }
 
 void
@@ -767,68 +1307,95 @@ ZenCacheDiskLayer::CacheBucket::GatherReferences(GcContext& GcCtx)
 {
 	ZEN_TRACE_CPU("Z$::DiskLayer::CacheBucket::GatherReferences");
 
-	Stopwatch  Timer;
-	const auto Guard = MakeGuard(
-		[this, &Timer] { ZEN_INFO("gathered references from '{}' in {}", m_BucketDir, NiceTimeSpanMs(Timer.GetElapsedTimeMs())); });
+	uint64_t WriteBlockTimeUs		 = 0;
+	uint64_t WriteBlockLongestTimeUs = 0;
+	uint64_t ReadBlockTimeUs		 = 0;
+	uint64_t ReadBlockLongestTimeUs	 = 0;
+
+	Stopwatch  TotalTimer;
+	const auto _ = MakeGuard([&] {
+		ZEN_INFO("gathered references from '{}' in {} write lock: {} ({}), read lock: {} ({})",
+				 m_BucketDir / m_BucketName,
+				 NiceTimeSpanMs(TotalTimer.GetElapsedTimeMs()),
+				 NiceLatencyNs(WriteBlockTimeUs),
+				 NiceLatencyNs(WriteBlockLongestTimeUs),
+				 NiceLatencyNs(ReadBlockTimeUs),
+				 NiceLatencyNs(ReadBlockLongestTimeUs));
+	});
 
 	const GcClock::TimePoint ExpireTime =
 		GcCtx.MaxCacheDuration() == GcClock::Duration::max() ? GcClock::TimePoint::min() : GcCtx.Time() - GcCtx.MaxCacheDuration();
 
 	const GcClock::Tick ExpireTicks = ExpireTime.time_since_epoch().count();
 
-	RwLock::SharedLockScope _(m_IndexLock);
-
-	std::vector<IoHash>				  ValidKeys;
-	std::vector<IoHash>				  ExpiredKeys;
-	std::vector<IoHash>				  Cids;
-	std::vector<IndexMap::value_type> Entries(m_Index.begin(), m_Index.end());
-
-	std::sort(Entries.begin(), Entries.end(), [](const auto& LHS, const auto& RHS) {
-		return LHS.second.LastAccess < RHS.second.LastAccess;
-	});
+	IndexMap Index;
+	{
+		RwLock::SharedLockScope __(m_IndexLock);
+		Stopwatch				Timer;
+		const auto				___ = MakeGuard([&] {
+			 uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
+			 WriteBlockTimeUs += ElapsedUs;
+			 WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
+		 });
+		Index						= m_Index;
+	}
 
-	const auto ValidIt = std::lower_bound(Entries.begin(), Entries.end(), ExpireTicks, [](const auto& Kv, auto Ticks) {
-		const IndexEntry& Entry = Kv.second;
-		return Entry.LastAccess < Ticks;
-	});
+	std::vector<IoHash> ExpiredKeys;
+	ExpiredKeys.reserve(1024);
 
+	std::vector<IoHash> Cids;
 	Cids.reserve(1024);
 
-	for (auto Kv = ValidIt; Kv != Entries.end(); ++Kv)
+	for (const auto& Entry : Index)
 	{
-		const IoHash&		Key = Kv->first;
-		const DiskLocation& Loc = Kv->second.Location;
+		const IoHash& Key = Entry.first;
+		if (Entry.second.LastAccess < ExpireTicks)
+		{
+			ExpiredKeys.push_back(Key);
+			continue;
+		}
+
+		const DiskLocation& Loc = Entry.second.Location;
 
 		if (Loc.IsFlagSet(DiskLocation::kStructured))
 		{
-			ZenCacheValue CacheValue;
-			if (!GetInlineCacheValue(Loc, CacheValue))
+			if (Cids.size() > 1024)
 			{
-				GetStandaloneCacheValue(Loc, Key, CacheValue);
+				GcCtx.ContributeCids(Cids);
+				Cids.clear();
 			}
 
-			if (CacheValue.Value)
+			ZenCacheValue CacheValue;
 			{
-				ZEN_ASSERT(CacheValue.Value.GetContentType() == ZenContentType::kCbObject);
-				if (Cids.size() > 1024)
+				RwLock::SharedLockScope __(m_IndexLock);
+				Stopwatch				Timer;
+				const auto				___ = MakeGuard([&] {
+					 uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
+					 WriteBlockTimeUs += ElapsedUs;
+					 WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
+				 });
+				if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
 				{
-					GcCtx.ContributeCids(Cids);
-					Cids.clear();
+					if (!GetStandaloneCacheValue(Loc, Key, CacheValue))
+					{
+						continue;
+					}
+				}
+				else if (!GetInlineCacheValue(Loc, CacheValue))
+				{
+					continue;
 				}
-				CbObject Obj(SharedBuffer{CacheValue.Value});
-				Obj.IterateAttachments([&Cids](CbFieldView Field) { Cids.push_back(Field.AsAttachment()); });
 			}
+
+			ZEN_ASSERT(CacheValue.Value);
+			ZEN_ASSERT(CacheValue.Value.GetContentType() == ZenContentType::kCbObject);
+			CbObject Obj(SharedBuffer{CacheValue.Value});
+			Obj.IterateAttachments([&Cids](CbFieldView Field) { Cids.push_back(Field.AsAttachment()); });
 		}
 	}
 
-	ValidKeys.reserve(std::distance(ValidIt, Entries.end()));
-	ExpiredKeys.reserve(std::distance(Entries.begin(), ValidIt));
-
-	std::transform(ValidIt, Entries.end(), std::back_inserter(ValidKeys), [](const auto& Kv) { return Kv.first; });
-	std::transform(Entries.begin(), ValidIt, std::back_inserter(ExpiredKeys), [](const auto& Kv) { return Kv.first; });
-
 	GcCtx.ContributeCids(Cids);
-	GcCtx.ContributeCacheKeys(m_BucketName, std::move(ValidKeys), std::move(ExpiredKeys));
+	GcCtx.ContributeCacheKeys(m_BucketName, std::move(ExpiredKeys));
 }
 
 void
@@ -836,203 +1403,282 @@ ZenCacheDiskLayer::CacheBucket::CollectGarbage(GcContext& GcCtx)
 {
 	ZEN_TRACE_CPU("Z$::DiskLayer::CacheBucket::CollectGarbage");
 
-	Flush();
-
-	RwLock::ExclusiveLockScope _(m_IndexLock);
-
-	const uint64_t OldCount		= m_Index.size();
-	const uint64_t OldTotalSize = m_TotalSize.load(std::memory_order::relaxed);
-
-	ZEN_INFO("collecting garbage from z$ bucket '{}'", m_BucketDir);
-
-	Stopwatch  Timer;
-	const auto Guard = MakeGuard([this, &Timer, &OldCount, &OldTotalSize] {
-		const uint64_t NewCount		= m_Index.size();
-		const uint64_t NewTotalSize = m_TotalSize.load(std::memory_order::relaxed);
-		ZEN_INFO("garbage collect from '{}' DONE after {}, collected {} ({}) chunks of total {} ({})",
-				 m_BucketDir,
-				 NiceTimeSpanMs(Timer.GetElapsedTimeMs()),
-				 OldCount - NewCount,
-				 NiceBytes(OldTotalSize - NewTotalSize),
-				 OldCount,
-				 NiceBytes(OldTotalSize));
+	ZEN_INFO("collecting garbage from '{}'", m_BucketDir / m_BucketName);
+
+	Stopwatch TotalTimer;
+	uint64_t  WriteBlockTimeUs		  = 0;
+	uint64_t  WriteBlockLongestTimeUs = 0;
+	uint64_t  ReadBlockTimeUs		  = 0;
+	uint64_t  ReadBlockLongestTimeUs  = 0;
+	uint64_t  TotalChunkCount		  = 0;
+	uint64_t  DeletedSize			  = 0;
+	uint64_t  OldTotalSize			  = m_TotalSize.load(std::memory_order::relaxed);
+
+	uint64_t DeletedCount = 0;
+	uint64_t MovedCount	  = 0;
+
+	const auto _ = MakeGuard([&] {
+		ZEN_INFO(
+			"garbage collect from '{}' DONE after {}, write lock: {} ({}), read lock: {} ({}), collected {} bytes, deleted #{} and moved "
+			"#{} "
+			"of #{} "
+			"entires ({}).",
+			m_BucketDir / m_BucketName,
+			NiceTimeSpanMs(TotalTimer.GetElapsedTimeMs()),
+			NiceLatencyNs(WriteBlockTimeUs),
+			NiceLatencyNs(WriteBlockLongestTimeUs),
+			NiceLatencyNs(ReadBlockTimeUs),
+			NiceLatencyNs(ReadBlockLongestTimeUs),
+			NiceBytes(DeletedSize),
+			DeletedCount,
+			MovedCount,
+			TotalChunkCount,
+			NiceBytes(OldTotalSize));
+		RwLock::SharedLockScope _(m_IndexLock);
 		SaveManifest();
 	});
 
-	if (m_Index.empty())
+	m_SlogFile.Flush();
+
+	std::span<const IoHash> ExpiredCacheKeys = GcCtx.ExpiredCacheKeys(m_BucketName);
+	std::vector<IoHash>		DeleteCacheKeys;
+	DeleteCacheKeys.reserve(ExpiredCacheKeys.size());
+	GcCtx.FilterCas(ExpiredCacheKeys, [&](const IoHash& ChunkHash, bool Keep) {
+		if (Keep)
+		{
+			return;
+		}
+		DeleteCacheKeys.push_back(ChunkHash);
+	});
+	if (DeleteCacheKeys.empty())
 	{
+		ZEN_INFO("garbage collect SKIPPED, for '{}', no expired cache keys found", m_BucketDir / m_BucketName);
 		return;
 	}
 
-	auto AddEntries = [this](std::span<const IoHash> Keys, std::vector<IndexMap::value_type>& OutEntries) {
-		for (const IoHash& Key : Keys)
+	std::vector<DiskIndexEntry>		 ExpiredStandaloneEntries;
+	IndexMap						 Index;
+	BlockStore::ReclaimSnapshotState BlockStoreState;
+	{
+		RwLock::SharedLockScope __(m_IndexLock);
+		Stopwatch				Timer;
+		const auto				____ = MakeGuard([&] {
+			 uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
+			 WriteBlockTimeUs += ElapsedUs;
+			 WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
+		 });
+		if (m_Index.empty())
 		{
-			if (auto It = m_Index.find(Key); It != m_Index.end())
-			{
-				OutEntries.push_back(*It);
-			}
+			ZEN_INFO("garbage collect SKIPPED, for '{}', container is empty", m_BucketDir / m_BucketName);
+			return;
 		}
-	};
+		BlockStoreState = m_BlockStore.GetReclaimSnapshotState();
 
-	std::vector<IndexMap::value_type> ValidEntries;
-	std::vector<IndexMap::value_type> ExpiredEntries;
-
-	AddEntries(GcCtx.ValidCacheKeys(m_BucketName), ValidEntries);
-	AddEntries(GcCtx.ExpiredCacheKeys(m_BucketName), ExpiredEntries);
-
-	// Remove all standalone file(s)
-	// NOTE: This can probably be made asynchronously
-	{
-		std::error_code			   Ec;
-		ExtendablePathBuilder<256> Path;
+		SaveManifest();
+		Index = m_Index;
 
-		for (const auto& Entry : ExpiredEntries)
+		for (const IoHash& Key : DeleteCacheKeys)
 		{
-			const IoHash&		Key = Entry.first;
-			const DiskLocation& Loc = Entry.second.Location;
-
-			if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
+			if (auto It = Index.find(Key); It != Index.end())
 			{
-				Path.Reset();
-				BuildPath(Path, Key);
-
-				// NOTE: this will update index and log file
-				DeleteStandaloneCacheValue(Loc, Key, Path.c_str(), Ec);
-
-				if (Ec)
+				DiskIndexEntry Entry = {.Key = It->first, .Location = It->second.Location};
+				if (Entry.Location.Flags & DiskLocation::kStandaloneFile)
 				{
-					ZEN_WARN("delete expired z$ standalone file '{}' FAILED, reason '{}'", Path.ToUtf8(), Ec.message());
-					Ec.clear();
+					Entry.Location.Flags |= DiskLocation::kTombStone;
+					ExpiredStandaloneEntries.push_back(Entry);
 				}
 			}
 		}
+		if (GcCtx.IsDeletionMode())
+		{
+			for (const auto& Entry : ExpiredStandaloneEntries)
+			{
+				m_Index.erase(Entry.Key);
+			}
+			m_SlogFile.Append(ExpiredStandaloneEntries);
+		}
 	}
 
-	if (GcCtx.CollectSmallObjects() && !ExpiredEntries.empty())
+	if (GcCtx.IsDeletionMode())
 	{
-		// Naive GC implementation of small objects. Needs enough free
-		// disk space to store intermediate sob container along side the
-		// old container
-
-		const auto ResetSobStorage = [this, &ValidEntries]() {
-			m_SobsFile.Close();
-			m_SlogFile.Close();
+		std::error_code			   Ec;
+		ExtendablePathBuilder<256> Path;
 
-			const bool IsNew = true;
-			m_SobsFile.Open(m_BucketDir / "zen.sobs", IsNew ? BasicFile::Mode::kTruncate : BasicFile::Mode::kWrite);
-			m_SlogFile.Open(m_BucketDir / "zen.slog", IsNew ? CasLogFile::Mode::kTruncate : CasLogFile::Mode::kWrite);
+		for (const auto& Entry : ExpiredStandaloneEntries)
+		{
+			const IoHash&		Key = Entry.Key;
+			const DiskLocation& Loc = Entry.Location;
 
-			m_SobsCursor = 0;
-			m_TotalSize	 = 0;
-			m_Index.clear();
+			Path.Reset();
+			BuildPath(Path, Key);
+			fs::path FilePath = Path.ToPath();
 
-			for (const auto& Entry : ValidEntries)
 			{
-				const IoHash&		Key = Entry.first;
-				const DiskLocation& Loc = Entry.second.Location;
+				RwLock::SharedLockScope __(m_IndexLock);
+				Stopwatch				Timer;
+				const auto				____ = MakeGuard([&] {
+					 uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
+					 WriteBlockTimeUs += ElapsedUs;
+					 WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
+				 });
+				if (m_Index.contains(Key))
+				{
+					// Someone added it back, let the file on disk be
+					ZEN_DEBUG("skipping z$ delete standalone of file '{}' FAILED, it has been added back", Path.ToUtf8());
+					continue;
+				}
+				__.ReleaseNow();
 
-				if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
+				RwLock::ExclusiveLockScope ValueLock(LockForHash(Key));
+				if (fs::is_regular_file(FilePath))
 				{
-					m_SlogFile.Append({.Key = Key, .Location = Loc});
-					m_Index.insert({Key, {Loc, GcClock::TickCount()}});
-					m_TotalSize.fetch_add(Loc.Size(), std::memory_order::relaxed);
+					ZEN_DEBUG("deleting standalone cache file '{}'", Path.ToUtf8());
+					fs::remove(FilePath, Ec);
 				}
 			}
-		};
 
-		uint64_t NewContainerSize{};
-		for (const auto& Entry : ValidEntries)
-		{
-			const DiskLocation& Loc = Entry.second.Location;
-
-			if (Loc.IsFlagSet(DiskLocation::kStandaloneFile) == false)
+			if (Ec)
 			{
-				NewContainerSize += (Loc.Size() + sizeof(DiskLocation));
+				ZEN_WARN("delete expired z$ standalone file '{}' FAILED, reason: '{}'", Path.ToUtf8(), Ec.message());
+				Ec.clear();
+				DiskLocation RestoreLocation = Loc;
+				RestoreLocation.Flags &= ~DiskLocation::kTombStone;
+
+				RwLock::ExclusiveLockScope __(m_IndexLock);
+				Stopwatch				   Timer;
+				const auto				   ___ = MakeGuard([&] {
+					uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
+					ReadBlockTimeUs += ElapsedUs;
+					ReadBlockLongestTimeUs = std::max(ElapsedUs, ReadBlockLongestTimeUs);
+				});
+				if (m_Index.contains(Key))
+				{
+					continue;
+				}
+				m_SlogFile.Append(DiskIndexEntry{.Key = Key, .Location = RestoreLocation});
+				m_Index.insert({Key, {Loc, GcClock::TickCount()}});
+				m_TotalSize.fetch_add(Entry.Location.Size(), std::memory_order::relaxed);
+				continue;
 			}
+			m_TotalSize.fetch_sub(Entry.Location.Size(), std::memory_order::relaxed);
+			DeletedSize += Entry.Location.Size();
+			DeletedCount++;
 		}
+	}
 
-		if (NewContainerSize == 0)
-		{
-			ResetSobStorage();
-			return;
-		}
+	TotalChunkCount = Index.size();
 
-		const uint64_t DiskSpaceMargin = (256 << 10);
+	std::vector<IoHash> TotalChunkHashes;
+	TotalChunkHashes.reserve(TotalChunkCount);
+	for (const auto& Entry : Index)
+	{
+		const DiskLocation& Location = Entry.second.Location;
 
-		std::error_code Ec;
-		DiskSpace		Space = DiskSpaceInfo(m_BucketDir, Ec);
-		if (Ec || Space.Free < NewContainerSize + DiskSpaceMargin)
+		if (Location.Flags & DiskLocation::kStandaloneFile)
 		{
-			ZEN_WARN("garbage collect z$ bucket '{}' FAILED, not enough disk space {}/{} (required/free)",
-					 m_BucketDir,
-					 NiceBytes(NewContainerSize),
-					 NiceBytes(Space.Free));
-			return;
+			continue;
 		}
+		TotalChunkHashes.push_back(Entry.first);
+	}
 
-		std::filesystem::path TmpSobsPath{m_BucketDir / "zen.sobs.tmp"};
-		std::filesystem::path TmpSlogPath{m_BucketDir / "zen.slog.tmp"};
-
-		// Copy non expired sob(s) to temporary sob container
-
+	if (TotalChunkHashes.empty())
+	{
+		return;
+	}
+	TotalChunkCount = TotalChunkHashes.size();
+
+	std::vector<BlockStoreLocation> ChunkLocations;
+	BlockStore::ChunkIndexArray		KeepChunkIndexes;
+	std::vector<IoHash>				ChunkIndexToChunkHash;
+	ChunkLocations.reserve(TotalChunkCount);
+	ChunkLocations.reserve(TotalChunkCount);
+	ChunkIndexToChunkHash.reserve(TotalChunkCount);
+
+	GcCtx.FilterCas(TotalChunkHashes, [&](const IoHash& ChunkHash, bool Keep) {
+		auto				KeyIt		 = Index.find(ChunkHash);
+		const DiskLocation& DiskLocation = KeyIt->second.Location;
+		BlockStoreLocation	Location	 = DiskLocation.GetBlockLocation(m_PayloadAlignment);
+		size_t				ChunkIndex	 = ChunkLocations.size();
+		ChunkLocations.push_back(Location);
+		ChunkIndexToChunkHash[ChunkIndex] = ChunkHash;
+		if (Keep)
 		{
-			BasicFile					TmpSobs;
-			TCasLogFile<DiskIndexEntry> TmpLog;
-			uint64_t					TmpCursor{};
-			std::vector<uint8_t>		Chunk;
+			KeepChunkIndexes.push_back(ChunkIndex);
+		}
+	});
 
-			TmpSobs.Open(TmpSobsPath, BasicFile::Mode::kTruncate);
-			TmpLog.Open(TmpSlogPath, CasLogFile::Mode::kTruncate);
+	size_t DeleteCount = TotalChunkCount - KeepChunkIndexes.size();
 
-			for (const auto& Entry : ValidEntries)
-			{
-				const IoHash&		Key = Entry.first;
-				const DiskLocation& Loc = Entry.second.Location;
+	const bool PerformDelete = GcCtx.IsDeletionMode() && GcCtx.CollectSmallObjects();
+	if (!PerformDelete)
+	{
+		m_BlockStore.ReclaimSpace(BlockStoreState, ChunkLocations, KeepChunkIndexes, m_PayloadAlignment, true);
+		uint64_t TotalSize = m_TotalSize.load(std::memory_order_relaxed);
+		ZEN_INFO("garbage collect from '{}' DISABLED, found #{} {} chunks of total #{} {}",
+				 m_BucketDir / m_BucketName,
+				 DeleteCount,
+				 0,	 // NiceBytes(TotalSize - NewTotalSize),
+				 TotalChunkCount,
+				 NiceBytes(TotalSize));
+		return;
+	}
 
-				DiskLocation NewLoc;
+	std::vector<IoHash> DeletedChunks;
+	m_BlockStore.ReclaimSpace(
+		BlockStoreState,
+		ChunkLocations,
+		KeepChunkIndexes,
+		m_PayloadAlignment,
+		false,
+		[&](const BlockStore::MovedChunksArray& MovedChunks, const BlockStore::ChunkIndexArray& RemovedChunks) {
+			std::vector<DiskIndexEntry> LogEntries;
+			LogEntries.reserve(MovedChunks.size() + RemovedChunks.size());
+			for (const auto& Entry : MovedChunks)
+			{
+				size_t					  ChunkIndex	  = Entry.first;
+				const BlockStoreLocation& NewLocation	  = Entry.second;
+				const IoHash&			  ChunkHash		  = ChunkIndexToChunkHash[ChunkIndex];
+				const DiskLocation&		  OldDiskLocation = Index[ChunkHash].Location;
+				LogEntries.push_back(
+					{.Key = ChunkHash, .Location = DiskLocation(NewLocation, m_PayloadAlignment, OldDiskLocation.GetFlags())});
+			}
+			for (const size_t ChunkIndex : RemovedChunks)
+			{
+				const IoHash&		ChunkHash		= ChunkIndexToChunkHash[ChunkIndex];
+				const DiskLocation& OldDiskLocation = Index[ChunkHash].Location;
+				LogEntries.push_back({.Key		= ChunkHash,
+									  .Location = DiskLocation(OldDiskLocation.GetBlockLocation(m_PayloadAlignment),
+															   m_PayloadAlignment,
+															   OldDiskLocation.GetFlags() | DiskLocation::kTombStone)});
+				DeletedChunks.push_back(ChunkHash);
+			}
 
-				if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
-				{
-					NewLoc = DiskLocation(0, Loc.Size(), 0, Loc.GetFlags());
-				}
-				else
+			m_SlogFile.Append(LogEntries);
+			m_SlogFile.Flush();
+			{
+				RwLock::ExclusiveLockScope __(m_IndexLock);
+				Stopwatch				   Timer;
+				const auto				   ____ = MakeGuard([&] {
+					uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
+					ReadBlockTimeUs += ElapsedUs;
+					ReadBlockLongestTimeUs = std::max(ElapsedUs, ReadBlockLongestTimeUs);
+				});
+				for (const DiskIndexEntry& Entry : LogEntries)
 				{
-					Chunk.resize(Loc.Size());
-					m_SobsFile.Read(Chunk.data(), Chunk.size(), Loc.Offset());
-
-					NewLoc = DiskLocation(TmpCursor, Chunk.size(), 0, Loc.GetFlags());
-					TmpSobs.Write(Chunk.data(), Chunk.size(), TmpCursor);
-					TmpCursor = RoundUp(TmpCursor + Chunk.size(), 16);
+					if (Entry.Location.GetFlags() & DiskLocation::kTombStone)
+					{
+						m_Index.erase(Entry.Key);
+						uint64_t ChunkSize = Entry.Location.GetBlockLocation(m_PayloadAlignment).Size;
+						m_TotalSize.fetch_sub(ChunkSize);
+						continue;
+					}
+					m_Index[Entry.Key].Location = Entry.Location;
 				}
-
-				TmpLog.Append(DiskIndexEntry{.Key = Key, .Location = NewLoc});
 			}
-		}
-
-		// Swap state
-		try
-		{
-			fs::path SobsPath{m_BucketDir / "zen.sobs"};
-			fs::path SlogPath{m_BucketDir / "zen.slog"};
-
-			m_SobsFile.Close();
-			m_SlogFile.Close();
-
-			fs::remove(SobsPath);
-			fs::remove(SlogPath);
-
-			fs::rename(TmpSobsPath, SobsPath);
-			fs::rename(TmpSlogPath, SlogPath);
+		},
+		[&]() { return GcCtx.CollectSmallObjects(); });
 
-			const bool IsNew = false;
-			OpenLog(m_BucketDir, IsNew);
-		}
-		catch (std::exception& Err)
-		{
-			ZEN_ERROR("garbage collection FAILED, reason '{}'", Err.what());
-			ResetSobStorage();
-		}
-	}
+	GcCtx.DeletedCas(DeletedChunks);
 }
 
 void
@@ -1079,96 +1725,187 @@ ZenCacheDiskLayer::UpdateAccessTimes(const zen::access_tracking::AccessTimes& Ac
 void
 ZenCacheDiskLayer::CacheBucket::PutStandaloneCacheValue(const IoHash& HashKey, const ZenCacheValue& Value)
 {
-	RwLock::ExclusiveLockScope ValueLock(LockForHash(HashKey));
-
-	ExtendablePathBuilder<256> DataFilePath;
-	BuildPath(DataFilePath, HashKey);
+	uint64_t NewFileSize = Value.Value.Size();
 
 	TemporaryFile DataFile;
 
 	std::error_code Ec;
 	DataFile.CreateTemporary(m_BucketDir.c_str(), Ec);
-
 	if (Ec)
 	{
-		throw std::system_error(Ec, fmt::format("Failed to open temporary file for put at '{}'", m_BucketDir));
-	}
+		throw std::system_error(Ec, fmt::format("Failed to open temporary file for put in '{}'", m_BucketDir));
+	}
+
+	bool CleanUpTempFile = false;
+	auto __				 = MakeGuard([&] {
+		 if (CleanUpTempFile)
+		 {
+			 std::error_code Ec;
+			 std::filesystem::remove(DataFile.GetPath(), Ec);
+			 if (Ec)
+			 {
+				 ZEN_WARN("Failed to clean up temporary file '{}' for put in '{}', reason '{}'",
+						  DataFile.GetPath(),
+						  m_BucketDir,
+						  Ec.message());
+			 }
+		 }
+	 });
 
 	DataFile.WriteAll(Value.Value, Ec);
-
 	if (Ec)
 	{
-		throw std::system_error(Ec, fmt::format("Failed to write payload ({} bytes) to file", NiceBytes(Value.Value.Size())));
+		throw std::system_error(Ec,
+								fmt::format("Failed to write payload ({} bytes) to temporary file '{}' for put in '{}'",
+											NiceBytes(NewFileSize),
+											DataFile.GetPath().string(),
+											m_BucketDir));
 	}
 
-	// Move file into place (atomically)
-
+	ExtendablePathBuilder<256> DataFilePath;
+	BuildPath(DataFilePath, HashKey);
 	std::filesystem::path FsPath{DataFilePath.ToPath()};
 
-	DataFile.MoveTemporaryIntoPlace(FsPath, Ec);
-
-	if (Ec)
+	// We retry to move the file since it can be held open for read.
+	// This happens if the server processes a Get request for the file or
+	// if we are busy sending the file upstream
+	int RetryCount = 4;
+	do
 	{
-		int RetryCount = 3;
-
-		do
+		Ec.clear();
 		{
-			std::filesystem::path ParentPath = FsPath.parent_path();
-			CreateDirectories(ParentPath);
+			RwLock::ExclusiveLockScope ValueLock(LockForHash(HashKey));
 
 			DataFile.MoveTemporaryIntoPlace(FsPath, Ec);
 
-			if (!Ec)
+			// Once we have called MoveTemporaryIntoPlace automatic clean up the temp file
+			// will be disabled as the file handle has already been closed
+			CleanUpTempFile = Ec ? true : false;
+
+			if (Ec)
 			{
-				break;
+				std::error_code ExistingEc;
+				uint64_t		OldFileSize = std::filesystem::file_size(FsPath, ExistingEc);
+				if (!ExistingEc && (OldFileSize == NewFileSize))
+				{
+					ZEN_INFO(
+						"Failed to move temporary file '{}' to '{}' for '{}'. Target file has same size, assuming concurrent write of same "
+						"value, "
+						"move "
+						"failed with reason '{}'",
+						DataFile.GetPath(),
+						FsPath.string(),
+						m_BucketDir,
+						Ec.message());
+					return;
+				}
 			}
+		}
 
-			std::error_code InnerEc;
-			const uint64_t	ExistingFileSize = std::filesystem::file_size(FsPath, InnerEc);
+		if (!Ec)
+		{
+			uint8_t EntryFlags = DiskLocation::kStandaloneFile;
 
-			if (!InnerEc && ExistingFileSize == Value.Value.Size())
+			if (Value.Value.GetContentType() == ZenContentType::kCbObject)
+			{
+				EntryFlags |= DiskLocation::kStructured;
+			}
+			else if (Value.Value.GetContentType() == ZenContentType::kCompressedBinary)
 			{
-				// Concurrent write of same value?
-				return;
+				EntryFlags |= DiskLocation::kCompressed;
 			}
 
-			// Semi arbitrary back-off
-			zen::Sleep(1000 * RetryCount);
-		} while (RetryCount--);
+			DiskLocation Loc(NewFileSize, EntryFlags);
+			IndexEntry	 Entry = IndexEntry(Loc, GcClock::TickCount());
 
-		if (Ec)
-		{
-			throw std::system_error(Ec, fmt::format("Failed to finalize file '{}'", DataFilePath.ToUtf8()));
+			uint64_t				   OldFileSize = 0;
+			RwLock::ExclusiveLockScope _(m_IndexLock);
+			if (auto It = m_Index.find(HashKey); It == m_Index.end())
+			{
+				// Previously unknown object
+				m_Index.insert({HashKey, Entry});
+			}
+			else
+			{
+				// TODO: should check if write is idempotent and bail out if it is?
+				OldFileSize = It.value().Location.Size();
+				It.value()	= Entry;
+			}
+
+			m_SlogFile.Append({.Key = HashKey, .Location = Loc});
+			if (OldFileSize <= NewFileSize)
+			{
+				m_TotalSize.fetch_add(NewFileSize - OldFileSize, std::memory_order::relaxed);
+			}
+			else
+			{
+				m_TotalSize.fetch_sub(OldFileSize - NewFileSize, std::memory_order::relaxed);
+			}
+			return;
 		}
-	}
 
-	// Update index
+		std::filesystem::path ParentPath = FsPath.parent_path();
+		if (!std::filesystem::is_directory(ParentPath))
+		{
+			Ec.clear();
+			std::filesystem::create_directories(ParentPath, Ec);
+			if (!Ec)
+			{
+				// Retry without sleep
+				continue;
+			}
+			throw std::system_error(
+				Ec,
+				fmt::format("Failed to create parent directory '{}' for file '{}' for put in '{}'", ParentPath, FsPath, m_BucketDir));
+		}
 
-	uint64_t EntryFlags = DiskLocation::kStandaloneFile;
+		ZEN_INFO("Failed renaming temporary file '{}' to '{}' for put in '{}', pausing and retrying, reason '{}'",
+				 DataFile.GetPath().string(),
+				 FsPath.string(),
+				 m_BucketDir,
+				 Ec.message());
 
-	if (Value.Value.GetContentType() == ZenContentType::kCbObject)
-	{
-		EntryFlags |= DiskLocation::kStructured;
-	}
+		// Semi arbitrary back-off
+		zen::Sleep(200 * (5 - RetryCount));	 // Sleep at most for a total of 3 seconds
+	} while (RetryCount-- > 0);
 
-	RwLock::ExclusiveLockScope _(m_IndexLock);
+	throw std::system_error(Ec, fmt::format("Failed to finalize file '{}' for put in '{}'", DataFilePath.ToUtf8(), m_BucketDir));
+}
 
-	DiskLocation Loc(/* Offset */ 0, Value.Value.Size(), 0, EntryFlags);
-	IndexEntry	 Entry = IndexEntry(Loc, GcClock::TickCount());
+void
+ZenCacheDiskLayer::CacheBucket::PutInlineCacheValue(const IoHash& HashKey, const ZenCacheValue& Value)
+{
+	uint8_t EntryFlags = 0;
 
-	if (auto It = m_Index.find(HashKey); It == m_Index.end())
+	if (Value.Value.GetContentType() == ZenContentType::kCbObject)
 	{
-		// Previously unknown object
-		m_Index.insert({HashKey, Entry});
+		EntryFlags |= DiskLocation::kStructured;
 	}
-	else
+	else if (Value.Value.GetContentType() == ZenContentType::kCompressedBinary)
 	{
-		// TODO: should check if write is idempotent and bail out if it is?
-		It.value() = Entry;
+		EntryFlags |= DiskLocation::kCompressed;
 	}
 
-	m_SlogFile.Append({.Key = HashKey, .Location = Loc});
-	m_TotalSize.fetch_add(Loc.Size(), std::memory_order::relaxed);
+	m_BlockStore.WriteChunk(Value.Value.Data(), Value.Value.Size(), m_PayloadAlignment, [&](const BlockStoreLocation& BlockStoreLocation) {
+		DiskLocation		 Location(BlockStoreLocation, m_PayloadAlignment, EntryFlags);
+		const DiskIndexEntry DiskIndexEntry{.Key = HashKey, .Location = Location};
+		m_SlogFile.Append(DiskIndexEntry);
+		RwLock::ExclusiveLockScope _(m_IndexLock);
+		if (auto It = m_Index.find(HashKey); It != m_Index.end())
+		{
+			// TODO: should check if write is idempotent and bail out if it is?
+			// this would requiring comparing contents on disk unless we add a
+			// content hash to the index entry
+			IndexEntry& Entry = It.value();
+			Entry.Location	  = Location;
+			Entry.LastAccess.store(GcClock::TickCount(), std::memory_order_relaxed);
+		}
+		else
+		{
+			m_Index.insert({HashKey, {Location, GcClock::TickCount()}});
+		}
+	});
+	m_TotalSize.fetch_add(Value.Value.Size(), std::memory_order::relaxed);
 }
 
 //////////////////////////////////////////////////////////////////////////
@@ -1255,10 +1992,10 @@ ZenCacheDiskLayer::Put(std::string_view InBucket, const IoHash& HashKey, const Z
 			auto It = m_Buckets.try_emplace(BucketName, BucketName);
 			Bucket	= &It.first->second;
 
-			std::filesystem::path bucketPath = m_RootDir;
-			bucketPath /= BucketName;
+			std::filesystem::path BucketPath = m_RootDir;
+			BucketPath /= BucketName;
 
-			Bucket->OpenOrCreate(bucketPath);
+			Bucket->OpenOrCreate(BucketPath);
 		}
 	}
 
@@ -1273,49 +2010,23 @@ ZenCacheDiskLayer::Put(std::string_view InBucket, const IoHash& HashKey, const Z
 void
 ZenCacheDiskLayer::DiscoverBuckets()
 {
-	FileSystemTraversal Traversal;
-	struct Visitor : public FileSystemTraversal::TreeVisitor
-	{
-		virtual void VisitFile([[maybe_unused]] const std::filesystem::path& Parent,
-							   [[maybe_unused]] const path_view&			 File,
-							   [[maybe_unused]] uint64_t					 FileSize) override
-		{
-		}
-
-		virtual bool VisitDirectory([[maybe_unused]] const std::filesystem::path& Parent, const path_view& DirectoryName) override
-		{
-			Dirs.push_back((decltype(Dirs)::value_type)(DirectoryName));
-			return false;
-		}
-
-		std::vector<std::filesystem::path::string_type> Dirs;
-	} Visit;
-
-	Traversal.TraverseFileSystem(m_RootDir, Visit);
+	DirectoryContent DirContent;
+	GetDirectoryContent(m_RootDir, DirectoryContent::IncludeDirsFlag, DirContent);
 
 	// Initialize buckets
 
 	RwLock::ExclusiveLockScope _(m_Lock);
 
-	for (const auto& BucketName : Visit.Dirs)
+	for (const std::filesystem::path& BucketPath : DirContent.Directories)
 	{
+		std::string BucketName = PathToUtf8(BucketPath.stem());
 		// New bucket needs to be created
-
-#if ZEN_PLATFORM_WINDOWS
-		std::string BucketName8 = WideToUtf8(BucketName);
-#else
-		const auto& BucketName8 = BucketName;
-#endif
-
-		if (auto It = m_Buckets.find(BucketName8); It != m_Buckets.end())
+		if (auto It = m_Buckets.find(BucketName); It != m_Buckets.end())
 		{
 		}
 		else
 		{
-			auto InsertResult = m_Buckets.try_emplace(BucketName8, BucketName8);
-
-			std::filesystem::path BucketPath = m_RootDir;
-			BucketPath /= BucketName8;
+			auto InsertResult = m_Buckets.try_emplace(BucketName, BucketName);
 
 			CacheBucket& Bucket = InsertResult.first->second;
 
@@ -1323,11 +2034,11 @@ ZenCacheDiskLayer::DiscoverBuckets()
 
 			if (Bucket.IsOk())
 			{
-				ZEN_INFO("Discovered bucket '{}'", BucketName8);
+				ZEN_INFO("Discovered bucket '{}'", BucketName);
 			}
 			else
 			{
-				ZEN_WARN("Found directory '{}' in our base directory '{}' but it is not a valid bucket", BucketName8, m_RootDir);
+				ZEN_WARN("Found directory '{}' in our base directory '{}' but it is not a valid bucket", BucketName, m_RootDir);
 
 				m_Buckets.erase(InsertResult.first);
 			}
@@ -1363,11 +2074,10 @@ void
 ZenCacheDiskLayer::Flush()
 {
 	std::vector<CacheBucket*> Buckets;
-	Buckets.reserve(m_Buckets.size());
 
 	{
 		RwLock::SharedLockScope _(m_Lock);
-
+		Buckets.reserve(m_Buckets.size());
 		for (auto& Kv : m_Buckets)
 		{
 			Buckets.push_back(&Kv.second);
@@ -1416,6 +2126,176 @@ ZenCacheDiskLayer::TotalSize() const
 	return TotalSize;
 }
 
+//////////////////////////// ZenCacheStore
+
+static constexpr std::string_view UE4DDCNamespaceName = "ue4.ddc";
+
+ZenCacheStore::ZenCacheStore(CasGc& Gc, std::filesystem::path BasePath) : GcStorage(Gc), GcContributor(Gc)
+{
+	CreateDirectories(BasePath);
+
+	DirectoryContent DirContent;
+	GetDirectoryContent(BasePath, DirectoryContent::IncludeDirsFlag, DirContent);
+
+	std::vector<std::string> LegacyBuckets;
+	std::vector<std::string> Namespaces;
+	for (const std::filesystem::path& DirPath : DirContent.Directories)
+	{
+		std::string DirName = PathToUtf8(DirPath.stem());
+		if (DirName.starts_with(NamespaceDiskPrefix))
+		{
+			Namespaces.push_back(DirName.substr(NamespaceDiskPrefix.length()));
+			continue;
+		}
+		LegacyBuckets.push_back(DirName);
+	}
+
+	ZEN_INFO("Found #{} namespaces in '{}' and #{} legacy buckets", Namespaces.size(), BasePath, LegacyBuckets.size());
+
+	if (std::find(Namespaces.begin(), Namespaces.end(), UE4DDCNamespaceName) == Namespaces.end())
+	{
+		// default (unspecified) and ue4-ddc namespace points to the same namespace instance
+
+		ZEN_INFO("Moving #{} legacy buckets to '{}' namespace", LegacyBuckets.size(), UE4DDCNamespaceName);
+
+		std::filesystem::path DefaultNamespaceFolder = BasePath / fmt::format("{}{}", NamespaceDiskPrefix, UE4DDCNamespaceName);
+		CreateDirectories(DefaultNamespaceFolder);
+
+		// Move any non-namespace folders into the default namespace folder
+		for (const std::string& DirName : LegacyBuckets)
+		{
+			std::filesystem::path LegacyFolder = BasePath / DirName;
+			std::filesystem::path NewPath	   = DefaultNamespaceFolder / DirName;
+			std::error_code		  Ec;
+			std::filesystem::rename(LegacyFolder, NewPath, Ec);
+			if (Ec)
+			{
+				ZEN_ERROR("Unable to move '{}' to '{}', reason '{}'", LegacyFolder, NewPath, Ec.message());
+			}
+		}
+		Namespaces.push_back(std::string(UE4DDCNamespaceName));
+	}
+
+	for (const std::string& NamespaceName : Namespaces)
+	{
+		m_Namespaces[NamespaceName] =
+			std::make_unique<ZenCacheNamespace>(Gc, BasePath / fmt::format("{}{}", NamespaceDiskPrefix, NamespaceName));
+	}
+}
+
+ZenCacheStore::~ZenCacheStore()
+{
+	m_Namespaces.clear();
+}
+
+bool
+ZenCacheStore::Get(std::string_view Namespace, std::string_view Bucket, const IoHash& HashKey, ZenCacheValue& OutValue)
+{
+	if (ZenCacheNamespace* Store = GetNamespace(Namespace); Store)
+	{
+		return Store->Get(Bucket, HashKey, OutValue);
+	}
+	ZEN_WARN("request for unknown namespace '{}' in ZenCacheStore::Get, bucket '{}', key '{}'", Namespace, Bucket, HashKey.ToHexString());
+	return false;
+}
+
+void
+ZenCacheStore::Put(std::string_view Namespace, std::string_view Bucket, const IoHash& HashKey, const ZenCacheValue& Value)
+{
+	if (ZenCacheNamespace* Store = GetNamespace(Namespace); Store)
+	{
+		return Store->Put(Bucket, HashKey, Value);
+	}
+	ZEN_WARN("request for unknown namespace '{}' in ZenCacheStore::Put, bucket '{}', key '{}'", Namespace, Bucket, HashKey.ToHexString());
+}
+
+bool
+ZenCacheStore::DropBucket(std::string_view Namespace, std::string_view Bucket)
+{
+	if (ZenCacheNamespace* Store = GetNamespace(Namespace); Store)
+	{
+		return Store->DropBucket(Bucket);
+	}
+	ZEN_WARN("request for unknown namespace '{}' in ZenCacheStore::Put, bucket '{}'", Namespace, Bucket);
+	return false;
+}
+
+void
+ZenCacheStore::Flush()
+{
+	IterateNamespaces([&](std::string_view, ZenCacheNamespace& Store) { Store.Flush(); });
+}
+
+void
+ZenCacheStore::Scrub(ScrubContext& Ctx)
+{
+	IterateNamespaces([&](std::string_view, ZenCacheNamespace& Store) { Store.Scrub(Ctx); });
+}
+
+ZenCacheNamespace*
+ZenCacheStore::GetNamespace(std::string_view Namespace)
+{
+	RwLock::SharedLockScope _(m_NamespacesLock);
+	if (auto It = m_Namespaces.find(std::string(Namespace)); It != m_Namespaces.end())
+	{
+		return It->second.get();
+	}
+	if (Namespace == DefaultNamespace)
+	{
+		if (auto It = m_Namespaces.find(std::string(UE4DDCNamespaceName)); It != m_Namespaces.end())
+		{
+			return It->second.get();
+		}
+	}
+	return nullptr;
+}
+
+void
+ZenCacheStore::IterateNamespaces(const std::function<void(std::string_view Namespace, ZenCacheNamespace& Store)>& Callback) const
+{
+	std::vector<std::pair<std::string, ZenCacheNamespace&> > Namespaces;
+	{
+		RwLock::SharedLockScope _(m_NamespacesLock);
+		Namespaces.reserve(m_Namespaces.size());
+		for (const auto& Entry : m_Namespaces)
+		{
+			if (Entry.first == DefaultNamespace)
+			{
+				continue;
+			}
+			Namespaces.push_back({Entry.first, *Entry.second});
+		}
+	}
+	for (auto& Entry : Namespaces)
+	{
+		Callback(Entry.first, Entry.second);
+	}
+}
+
+void
+ZenCacheStore::GatherReferences(GcContext& GcCtx)
+{
+	IterateNamespaces([&](std::string_view, ZenCacheNamespace& Store) { Store.GatherReferences(GcCtx); });
+}
+
+void
+ZenCacheStore::CollectGarbage(GcContext& GcCtx)
+{
+	IterateNamespaces([&](std::string_view, ZenCacheNamespace& Store) { Store.CollectGarbage(GcCtx); });
+}
+
+GcStorageSize
+ZenCacheStore::StorageSize() const
+{
+	GcStorageSize Size;
+	IterateNamespaces([&](std::string_view, ZenCacheNamespace& Store) {
+		GcStorageSize StoreSize = Store.StorageSize();
+		Size.MemorySize += StoreSize.MemorySize;
+		Size.DiskSize += StoreSize.DiskSize;
+	});
+	return Size;
+}
+
 //////////////////////////////////////////////////////////////////////////
 
 #if ZEN_WITH_TESTS
@@ -1427,10 +2307,18 @@ namespace testutils {
 
 	IoBuffer CreateBinaryCacheValue(uint64_t Size)
 	{
-		std::vector<uint32_t> Data(size_t(Size / sizeof(uint32_t)));
-		std::generate(Data.begin(), Data.end(), [Idx = 0]() mutable { return Idx++; });
+		static std::random_device rd;
+		static std::mt19937		  g(rd());
+
+		std::vector<uint8_t> Values;
+		Values.resize(Size);
+		for (size_t Idx = 0; Idx < Size; ++Idx)
+		{
+			Values[Idx] = static_cast<uint8_t>(Idx);
+		}
+		std::shuffle(Values.begin(), Values.end(), g);
 
-		IoBuffer Buf(IoBuffer::Clone, Data.data(), Data.size() * sizeof(uint32_t));
+		IoBuffer Buf(IoBuffer::Clone, Values.data(), Values.size());
 		Buf.SetContentType(ZenContentType::kBinary);
 		return Buf;
 	};
@@ -1443,7 +2331,7 @@ TEST_CASE("z$.store")
 
 	CasGc Gc;
 
-	ZenCacheStore Zcs(Gc, TempDir.Path() / "cache");
+	ZenCacheNamespace Zcs(Gc, TempDir.Path() / "cache");
 
 	const int kIterationCount = 100;
 
@@ -1496,8 +2384,8 @@ TEST_CASE("z$.size")
 		GcStorageSize CacheSize;
 
 		{
-			CasGc		  Gc;
-			ZenCacheStore Zcs(Gc, TempDir.Path() / "cache");
+			CasGc			  Gc;
+			ZenCacheNamespace Zcs(Gc, TempDir.Path() / "cache");
 
 			CbObject CacheValue = CreateCacheValue(Zcs.DiskLayerThreshold() - 256);
 
@@ -1516,8 +2404,8 @@ TEST_CASE("z$.size")
 		}
 
 		{
-			CasGc		  Gc;
-			ZenCacheStore Zcs(Gc, TempDir.Path() / "cache");
+			CasGc			  Gc;
+			ZenCacheNamespace Zcs(Gc, TempDir.Path() / "cache");
 
 			const GcStorageSize SerializedSize = Zcs.StorageSize();
 			CHECK_EQ(SerializedSize.MemorySize, 0);
@@ -1539,8 +2427,8 @@ TEST_CASE("z$.size")
 		GcStorageSize CacheSize;
 
 		{
-			CasGc		  Gc;
-			ZenCacheStore Zcs(Gc, TempDir.Path() / "cache");
+			CasGc			  Gc;
+			ZenCacheNamespace Zcs(Gc, TempDir.Path() / "cache");
 
 			CbObject CacheValue = CreateCacheValue(Zcs.DiskLayerThreshold() + 64);
 
@@ -1559,8 +2447,8 @@ TEST_CASE("z$.size")
 		}
 
 		{
-			CasGc		  Gc;
-			ZenCacheStore Zcs(Gc, TempDir.Path() / "cache");
+			CasGc			  Gc;
+			ZenCacheNamespace Zcs(Gc, TempDir.Path() / "cache");
 
 			const GcStorageSize SerializedSize = Zcs.StorageSize();
 			CHECK_EQ(SerializedSize.MemorySize, 0);
@@ -1597,9 +2485,9 @@ TEST_CASE("z$.gc")
 		};
 
 		{
-			CasGc		  Gc;
-			ZenCacheStore Zcs(Gc, TempDir.Path() / "cache");
-			const auto	  Bucket = "teardrinker"sv;
+			CasGc			  Gc;
+			ZenCacheNamespace Zcs(Gc, TempDir.Path() / "cache");
+			const auto		  Bucket = "teardrinker"sv;
 
 			// Create a cache record
 			const IoHash   Key = CreateKey(42);
@@ -1635,7 +2523,7 @@ TEST_CASE("z$.gc")
 		// Expect timestamps to be serialized
 		{
 			CasGc				Gc;
-			ZenCacheStore		Zcs(Gc, TempDir.Path() / "cache");
+			ZenCacheNamespace	Zcs(Gc, TempDir.Path() / "cache");
 			std::vector<IoHash> Keep;
 
 			// Collect garbage with 1 hour max cache duration
@@ -1656,7 +2544,7 @@ TEST_CASE("z$.gc")
 	{
 		ScopedTemporaryDirectory TempDir;
 		CasGc					 Gc;
-		ZenCacheStore			 Zcs(Gc, TempDir.Path() / "cache");
+		ZenCacheNamespace		 Zcs(Gc, TempDir.Path() / "cache");
 		const auto				 Bucket		 = "fortysixandtwo"sv;
 		const GcClock::TimePoint CurrentTime = GcClock::Now();
 
@@ -1704,7 +2592,7 @@ TEST_CASE("z$.gc")
 	{
 		ScopedTemporaryDirectory TempDir;
 		CasGc					 Gc;
-		ZenCacheStore			 Zcs(Gc, TempDir.Path() / "cache");
+		ZenCacheNamespace		 Zcs(Gc, TempDir.Path() / "cache");
 		const auto				 Bucket		 = "rightintwo"sv;
 		const GcClock::TimePoint CurrentTime = GcClock::Now();
 
@@ -1737,6 +2625,7 @@ TEST_CASE("z$.gc")
 			GcCtx.MaxCacheDuration(std::chrono::minutes(2));
 			GcCtx.CollectSmallObjects(true);
 
+			Zcs.Flush();
 			Gc.CollectGarbage(GcCtx);
 
 			for (const auto& Key : Keys)
@@ -1751,6 +2640,502 @@ TEST_CASE("z$.gc")
 	}
 }
 
+TEST_CASE("z$.legacyconversion")
+{
+	ScopedTemporaryDirectory TempDir;
+
+	uint64_t			  ChunkSizes[]	  = {2041,
+							 1123,
+							 1223,
+							 1239,
+							 341,
+							 1412,
+							 912,
+							 774,
+							 341,
+							 431,
+							 554,
+							 1098,
+							 2048,
+							 339 + 64 * 1024,
+							 561 + 64 * 1024,
+							 16 + 64 * 1024,
+							 16 + 64 * 1024,
+							 2048,
+							 2048};
+	size_t				  ChunkCount	  = sizeof(ChunkSizes) / sizeof(uint64_t);
+	size_t				  SingleBlockSize = 0;
+	std::vector<IoBuffer> Chunks;
+	Chunks.reserve(ChunkCount);
+	for (uint64_t Size : ChunkSizes)
+	{
+		Chunks.push_back(testutils::CreateBinaryCacheValue(Size));
+		SingleBlockSize += Size;
+	}
+
+	std::vector<IoHash> ChunkHashes;
+	ChunkHashes.reserve(ChunkCount);
+	for (const IoBuffer& Chunk : Chunks)
+	{
+		ChunkHashes.push_back(IoHash::HashBuffer(Chunk.Data(), Chunk.Size()));
+	}
+
+	CreateDirectories(TempDir.Path());
+
+	const std::string Bucket = "rightintwo";
+	{
+		CasGc					 Gc;
+		ZenCacheNamespace		 Zcs(Gc, TempDir.Path());
+		const GcClock::TimePoint CurrentTime = GcClock::Now();
+
+		for (size_t i = 0; i < ChunkCount; i++)
+		{
+			Zcs.Put(Bucket, ChunkHashes[i], {.Value = Chunks[i]});
+		}
+
+		std::vector<IoHash> KeepChunks;
+		for (size_t i = 0; i < ChunkCount; i += 2)
+		{
+			KeepChunks.push_back(ChunkHashes[i]);
+		}
+		GcContext GcCtx(CurrentTime + std::chrono::hours(2));
+		GcCtx.MaxCacheDuration(std::chrono::minutes(2));
+		GcCtx.CollectSmallObjects(true);
+		GcCtx.ContributeCas(KeepChunks);
+		Zcs.Flush();
+		Gc.CollectGarbage(GcCtx);
+	}
+	std::filesystem::path BucketDir		= TempDir.Path() / Bucket;
+	std::filesystem::path BlocksBaseDir = BucketDir / "blocks";
+
+	std::filesystem::path CasPath		 = BlockStore ::GetBlockPath(BlocksBaseDir, 1);
+	std::filesystem::path LegacyDataPath = GetLegacyDataPath(BucketDir);
+	std::filesystem::remove(LegacyDataPath);
+	std::filesystem::rename(CasPath, LegacyDataPath);
+
+	std::vector<DiskIndexEntry> LogEntries;
+	std::filesystem::path		IndexPath = GetIndexPath(BucketDir, Bucket);
+	if (std::filesystem::is_regular_file(IndexPath))
+	{
+		BasicFile ObjectIndexFile;
+		ObjectIndexFile.Open(IndexPath, BasicFile::Mode::kRead);
+		uint64_t Size = ObjectIndexFile.FileSize();
+		if (Size >= sizeof(CacheBucketIndexHeader))
+		{
+			uint64_t			   ExpectedEntryCount = (Size - sizeof(sizeof(CacheBucketIndexHeader))) / sizeof(DiskIndexEntry);
+			CacheBucketIndexHeader Header;
+			ObjectIndexFile.Read(&Header, sizeof(Header), 0);
+			if (Header.Magic == CacheBucketIndexHeader::ExpectedMagic && Header.Version == CacheBucketIndexHeader::CurrentVersion &&
+				Header.PayloadAlignment > 0 && Header.EntryCount == ExpectedEntryCount)
+			{
+				LogEntries.resize(Header.EntryCount);
+				ObjectIndexFile.Read(LogEntries.data(), Header.EntryCount * sizeof(DiskIndexEntry), sizeof(CacheBucketIndexHeader));
+			}
+		}
+		ObjectIndexFile.Close();
+		std::filesystem::remove(IndexPath);
+	}
+
+	std::filesystem::path LogPath = GetLogPath(BucketDir, Bucket);
+	{
+		TCasLogFile<DiskIndexEntry> CasLog;
+		CasLog.Open(LogPath, CasLogFile::Mode::kRead);
+		LogEntries.reserve(CasLog.GetLogCount());
+		CasLog.Replay([&](const DiskIndexEntry& Record) { LogEntries.push_back(Record); }, 0);
+	}
+	TCasLogFile<LegacyDiskIndexEntry> LegacyLog;
+	std::filesystem::path			  LegacylogPath = GetLegacyLogPath(BucketDir);
+	LegacyLog.Open(LegacylogPath, CasLogFile::Mode::kTruncate);
+
+	for (const DiskIndexEntry& Entry : LogEntries)
+	{
+		uint64_t Size;
+		uint64_t Offset;
+		if (Entry.Location.IsFlagSet(DiskLocation::kStandaloneFile))
+		{
+			Size   = Entry.Location.Location.StandaloneSize;
+			Offset = 0;
+		}
+		else
+		{
+			BlockStoreLocation Location = Entry.Location.GetBlockLocation(16);
+			Size						= Location.Size;
+			Offset						= Location.Offset;
+		}
+		LegacyDiskLocation	 LegacyLocation(Offset, Size, 0, static_cast<uint64_t>(Entry.Location.Flags) << 56);
+		LegacyDiskIndexEntry LegacyEntry = {.Key = Entry.Key, .Location = LegacyLocation};
+		LegacyLog.Append(LegacyEntry);
+	}
+	LegacyLog.Close();
+
+	std::filesystem::remove_all(BlocksBaseDir);
+	std::filesystem::remove(LogPath);
+	std::filesystem::remove(IndexPath);
+
+	{
+		CasGc			  Gc;
+		ZenCacheNamespace Zcs(Gc, TempDir.Path());
+
+		for (size_t i = 0; i < ChunkCount; i += 2)
+		{
+			ZenCacheValue Value;
+			CHECK(Zcs.Get(Bucket, ChunkHashes[i], Value));
+			CHECK(ChunkHashes[i] == IoHash::HashBuffer(Value.Value));
+			CHECK(!Zcs.Get(Bucket, ChunkHashes[i + 1], Value));
+		}
+	}
+}
+
+TEST_CASE("z$.threadedinsert")	// * doctest::skip(true))
+{
+	//	for (uint32_t i = 0; i < 100; ++i)
+	{
+		ScopedTemporaryDirectory TempDir;
+
+		const uint64_t kChunkSize  = 1048;
+		const int32_t  kChunkCount = 8192;
+
+		struct Chunk
+		{
+			std::string Bucket;
+			IoBuffer	Buffer;
+		};
+		std::unordered_map<IoHash, Chunk, IoHash::Hasher> Chunks;
+		Chunks.reserve(kChunkCount);
+
+		const std::string Bucket1 = "rightinone";
+		const std::string Bucket2 = "rightintwo";
+
+		for (int32_t Idx = 0; Idx < kChunkCount; ++Idx)
+		{
+			while (true)
+			{
+				IoBuffer Chunk = testutils::CreateBinaryCacheValue(kChunkSize);
+				IoHash	 Hash  = HashBuffer(Chunk);
+				if (Chunks.contains(Hash))
+				{
+					continue;
+				}
+				Chunks[Hash] = {.Bucket = Bucket1, .Buffer = Chunk};
+				break;
+			}
+			while (true)
+			{
+				IoBuffer Chunk = testutils::CreateBinaryCacheValue(kChunkSize);
+				IoHash	 Hash  = HashBuffer(Chunk);
+				if (Chunks.contains(Hash))
+				{
+					continue;
+				}
+				Chunks[Hash] = {.Bucket = Bucket2, .Buffer = Chunk};
+				break;
+			}
+		}
+
+		CreateDirectories(TempDir.Path());
+
+		WorkerThreadPool  ThreadPool(4);
+		CasGc			  Gc;
+		ZenCacheNamespace Zcs(Gc, TempDir.Path());
+
+		{
+			std::atomic<size_t> WorkCompleted = 0;
+			for (const auto& Chunk : Chunks)
+			{
+				ThreadPool.ScheduleWork([&Zcs, &WorkCompleted, &Chunk]() {
+					Zcs.Put(Chunk.second.Bucket, Chunk.first, {.Value = Chunk.second.Buffer});
+					WorkCompleted.fetch_add(1);
+				});
+			}
+			while (WorkCompleted < Chunks.size())
+			{
+				Sleep(1);
+			}
+		}
+
+		const uint64_t TotalSize = Zcs.StorageSize().DiskSize;
+		CHECK_EQ(kChunkSize * Chunks.size(), TotalSize);
+
+		{
+			std::atomic<size_t> WorkCompleted = 0;
+			for (const auto& Chunk : Chunks)
+			{
+				ThreadPool.ScheduleWork([&Zcs, &WorkCompleted, &Chunk]() {
+					std::string	  Bucket	= Chunk.second.Bucket;
+					IoHash		  ChunkHash = Chunk.first;
+					ZenCacheValue CacheValue;
+
+					CHECK(Zcs.Get(Bucket, ChunkHash, CacheValue));
+					IoHash Hash = IoHash::HashBuffer(CacheValue.Value);
+					CHECK(ChunkHash == Hash);
+					WorkCompleted.fetch_add(1);
+				});
+			}
+			while (WorkCompleted < Chunks.size())
+			{
+				Sleep(1);
+			}
+		}
+		std::unordered_map<IoHash, std::string, IoHash::Hasher> GcChunkHashes;
+		GcChunkHashes.reserve(Chunks.size());
+		for (const auto& Chunk : Chunks)
+		{
+			GcChunkHashes[Chunk.first] = Chunk.second.Bucket;
+		}
+		{
+			std::unordered_map<IoHash, Chunk, IoHash::Hasher> NewChunks;
+
+			for (int32_t Idx = 0; Idx < kChunkCount; ++Idx)
+			{
+				{
+					IoBuffer Chunk	= testutils::CreateBinaryCacheValue(kChunkSize);
+					IoHash	 Hash	= HashBuffer(Chunk);
+					NewChunks[Hash] = {.Bucket = Bucket1, .Buffer = Chunk};
+				}
+				{
+					IoBuffer Chunk	= testutils::CreateBinaryCacheValue(kChunkSize);
+					IoHash	 Hash	= HashBuffer(Chunk);
+					NewChunks[Hash] = {.Bucket = Bucket2, .Buffer = Chunk};
+				}
+			}
+
+			std::atomic<size_t>	 WorkCompleted	 = 0;
+			std::atomic_uint32_t AddedChunkCount = 0;
+			for (const auto& Chunk : NewChunks)
+			{
+				ThreadPool.ScheduleWork([&Zcs, &WorkCompleted, Chunk, &AddedChunkCount]() {
+					Zcs.Put(Chunk.second.Bucket, Chunk.first, {.Value = Chunk.second.Buffer});
+					AddedChunkCount.fetch_add(1);
+					WorkCompleted.fetch_add(1);
+				});
+			}
+
+			for (const auto& Chunk : Chunks)
+			{
+				ThreadPool.ScheduleWork([&Zcs, &WorkCompleted, Chunk]() {
+					ZenCacheValue CacheValue;
+					if (Zcs.Get(Chunk.second.Bucket, Chunk.first, CacheValue))
+					{
+						CHECK(Chunk.first == IoHash::HashBuffer(CacheValue.Value));
+					}
+					WorkCompleted.fetch_add(1);
+				});
+			}
+			while (AddedChunkCount.load() < NewChunks.size())
+			{
+				// Need to be careful since we might GC blocks we don't know outside of RwLock::ExclusiveLockScope
+				for (const auto& Chunk : NewChunks)
+				{
+					ZenCacheValue CacheValue;
+					if (Zcs.Get(Chunk.second.Bucket, Chunk.first, CacheValue))
+					{
+						GcChunkHashes[Chunk.first] = Chunk.second.Bucket;
+					}
+				}
+				std::vector<IoHash> KeepHashes;
+				KeepHashes.reserve(GcChunkHashes.size());
+				for (const auto& Entry : GcChunkHashes)
+				{
+					KeepHashes.push_back(Entry.first);
+				}
+				size_t C = 0;
+				while (C < KeepHashes.size())
+				{
+					if (C % 155 == 0)
+					{
+						if (C < KeepHashes.size() - 1)
+						{
+							KeepHashes[C] = KeepHashes[KeepHashes.size() - 1];
+							KeepHashes.pop_back();
+						}
+						if (C + 3 < KeepHashes.size() - 1)
+						{
+							KeepHashes[C + 3] = KeepHashes[KeepHashes.size() - 1];
+							KeepHashes.pop_back();
+						}
+					}
+					C++;
+				}
+
+				GcContext GcCtx;
+				GcCtx.CollectSmallObjects(true);
+				GcCtx.ContributeCas(KeepHashes);
+				Zcs.CollectGarbage(GcCtx);
+				CasChunkSet& Deleted = GcCtx.DeletedCas();
+				Deleted.IterateChunks([&GcChunkHashes](const IoHash& ChunkHash) { GcChunkHashes.erase(ChunkHash); });
+			}
+
+			while (WorkCompleted < NewChunks.size() + Chunks.size())
+			{
+				Sleep(1);
+			}
+
+			{
+				// Need to be careful since we might GC blocks we don't know outside of RwLock::ExclusiveLockScope
+				for (const auto& Chunk : NewChunks)
+				{
+					ZenCacheValue CacheValue;
+					if (Zcs.Get(Chunk.second.Bucket, Chunk.first, CacheValue))
+					{
+						GcChunkHashes[Chunk.first] = Chunk.second.Bucket;
+					}
+				}
+				std::vector<IoHash> KeepHashes;
+				KeepHashes.reserve(GcChunkHashes.size());
+				for (const auto& Entry : GcChunkHashes)
+				{
+					KeepHashes.push_back(Entry.first);
+				}
+				size_t C = 0;
+				while (C < KeepHashes.size())
+				{
+					if (C % 155 == 0)
+					{
+						if (C < KeepHashes.size() - 1)
+						{
+							KeepHashes[C] = KeepHashes[KeepHashes.size() - 1];
+							KeepHashes.pop_back();
+						}
+						if (C + 3 < KeepHashes.size() - 1)
+						{
+							KeepHashes[C + 3] = KeepHashes[KeepHashes.size() - 1];
+							KeepHashes.pop_back();
+						}
+					}
+					C++;
+				}
+
+				GcContext GcCtx;
+				GcCtx.CollectSmallObjects(true);
+				GcCtx.ContributeCas(KeepHashes);
+				Zcs.CollectGarbage(GcCtx);
+				CasChunkSet& Deleted = GcCtx.DeletedCas();
+				Deleted.IterateChunks([&GcChunkHashes](const IoHash& ChunkHash) { GcChunkHashes.erase(ChunkHash); });
+			}
+		}
+		{
+			std::atomic<size_t> WorkCompleted = 0;
+			for (const auto& Chunk : GcChunkHashes)
+			{
+				ThreadPool.ScheduleWork([&Zcs, &WorkCompleted, Chunk]() {
+					ZenCacheValue CacheValue;
+					CHECK(Zcs.Get(Chunk.second, Chunk.first, CacheValue));
+					CHECK(Chunk.first == IoHash::HashBuffer(CacheValue.Value));
+					WorkCompleted.fetch_add(1);
+				});
+			}
+			while (WorkCompleted < GcChunkHashes.size())
+			{
+				Sleep(1);
+			}
+		}
+	}
+}
+
+TEST_CASE("z$.namespaces")
+{
+	using namespace testutils;
+
+	const auto CreateCacheValue = [](size_t Size) -> CbObject {
+		std::vector<uint8_t> Buf;
+		Buf.resize(Size);
+
+		CbObjectWriter Writer;
+		Writer.AddBinary("Binary"sv, Buf.data(), Buf.size());
+		return Writer.Save();
+	};
+
+	ScopedTemporaryDirectory TempDir;
+	CreateDirectories(TempDir.Path());
+
+	{
+		CasGc		  Gc;
+		ZenCacheStore Zcs(Gc, TempDir.Path() / "cache");
+		const auto	  Bucket		  = "teardrinker"sv;
+		const auto	  CustomNamespace = "mynamespace"sv;
+
+		// Create a cache record
+		const IoHash Key		= CreateKey(42);
+		CbObject	 CacheValue = CreateCacheValue(4096);
+
+		IoBuffer Buffer = CacheValue.GetBuffer().AsIoBuffer();
+		Buffer.SetContentType(ZenContentType::kCbObject);
+
+		ZenCacheValue PutValue = {.Value = Buffer};
+		Zcs.Put(ZenCacheStore::DefaultNamespace, Bucket, Key, PutValue);
+
+		ZenCacheValue GetValue;
+		CHECK(Zcs.Get(ZenCacheStore::DefaultNamespace, Bucket, Key, GetValue));
+
+		CHECK(!Zcs.Get(CustomNamespace, Bucket, Key, GetValue));
+
+		// This should just be dropped for now until we decide how we add namespaces
+		Zcs.Put(CustomNamespace, Bucket, Key, PutValue);
+		CHECK(!Zcs.Get(CustomNamespace, Bucket, Key, GetValue));
+
+		const IoHash Key2		 = CreateKey(43);
+		CbObject	 CacheValue2 = CreateCacheValue(4096);
+
+		IoBuffer Buffer2 = CacheValue2.GetBuffer().AsIoBuffer();
+		Buffer2.SetContentType(ZenContentType::kCbObject);
+		ZenCacheValue PutValue2 = {.Value = Buffer2};
+		Zcs.Put(CustomNamespace, Bucket, Key2, PutValue2);
+
+		CHECK(!Zcs.Get(ZenCacheStore::DefaultNamespace, Bucket, Key2, GetValue));
+	}
+}
+
+TEST_CASE("z$.blocked.disklayer.put")
+{
+	ScopedTemporaryDirectory TempDir;
+
+	GcStorageSize CacheSize;
+
+	const auto CreateCacheValue = [](size_t Size) -> CbObject {
+		std::vector<uint8_t> Buf;
+		Buf.resize(Size);
+
+		CbObjectWriter Writer;
+		Writer.AddBinary("Binary"sv, Buf.data(), Buf.size());
+		return Writer.Save();
+	};
+
+	CasGc			  Gc;
+	ZenCacheNamespace Zcs(Gc, TempDir.Path() / "cache");
+
+	CbObject CacheValue = CreateCacheValue(64 * 1024 + 64);
+
+	IoBuffer Buffer = CacheValue.GetBuffer().AsIoBuffer();
+	Buffer.SetContentType(ZenContentType::kCbObject);
+
+	size_t Key	   = Buffer.Size();
+	IoHash HashKey = IoHash::HashBuffer(&Key, sizeof(uint32_t));
+	Zcs.Put("test_bucket", HashKey, {.Value = Buffer});
+
+	ZenCacheValue BufferGet;
+	CHECK(Zcs.Get("test_bucket", HashKey, BufferGet));
+
+	// Overwriting with a value of same size should go fine
+	Zcs.Put("test_bucket", HashKey, {.Value = Buffer});
+
+	CbObject CacheValue2 = CreateCacheValue(64 * 1024 + 64 + 1);
+	IoBuffer Buffer2	 = CacheValue2.GetBuffer().AsIoBuffer();
+	Buffer2.SetContentType(ZenContentType::kCbObject);
+#	if ZEN_PLATFORM_WINDOWS
+	// On Windows platform, overwriting with different size while we have
+	// it open for read should throw exception if file is held open
+	CHECK_THROWS(Zcs.Put("test_bucket", HashKey, {.Value = Buffer2}));
+#	else
+	// Other platforms should handle overwrite just fine
+	Zcs.Put("test_bucket", HashKey, {.Value = Buffer2});
+#	endif
+
+	BufferGet = ZenCacheValue{};
+
+	// Read access has been removed, we should now be able to overwrite it
+	Zcs.Put("test_bucket", HashKey, {.Value = Buffer2});
+}
+
 #endif
 
 void