Use blocks to store data in cas stores

1 files changed, 723 insertions, 237 deletions

diff --git a/zenstore/compactcas.cpp b/zenstore/compactcas.cpp
index 91ee232fe..18dcc7fc8 100644
--- a/zenstore/compactcas.cpp
+++ b/zenstore/compactcas.cpp
@@ -2,27 +2,18 @@
 
 #include <zenstore/cas.h>
 
-#include "compactcas.h"
-
-#include <zencore/compactbinarybuilder.h>
-#include <zencore/except.h>
 #include <zencore/filesystem.h>
 #include <zencore/fmtutils.h>
 #include <zencore/logging.h>
-#include <zencore/memory.h>
-#include <zencore/string.h>
 #include <zencore/testing.h>
-#include <zencore/testutils.h>
-#include <zencore/thread.h>
-#include <zencore/uid.h>
-
 #include <zenstore/gc.h>
-
-#include <filesystem>
-#include <functional>
 #include <gsl/gsl-lite.hpp>
+#include "compactcas.h"
 
 #if ZEN_WITH_TESTS
+#	include <zencore/compactbinarybuilder.h>
+#	include <zencore/testutils.h>
+#	include <zenstore/cidstore.h>
 #	include <algorithm>
 #	include <random>
 #endif
@@ -31,11 +22,16 @@
 
 namespace zen {
 
-static uint64_t
-AlignPositon(uint64_t Offset, uint64_t Alignment)
-{
-	return (Offset + Alignment - 1) & ~(Alignment - 1);
-}
+namespace {
+	uint64_t AlignPositon(uint64_t Offset, uint64_t Alignment) { return (Offset + Alignment - 1) & ~(Alignment - 1); }
+
+	std::filesystem::path BuildUcasPath(const std::filesystem::path& RootDirectory,
+										const std::string_view		 ContainerBaseName,
+										const uint16_t				 BlockIndex)
+	{
+		return RootDirectory / (std::string(ContainerBaseName) + "." + (std::to_string(BlockIndex) + ".ucas"));
+	}
+}  // namespace
 
 CasContainerStrategy::CasContainerStrategy(const CasStoreConfiguration& Config, CasGc& Gc)
 : GcStorage(Gc)
@@ -49,13 +45,15 @@ CasContainerStrategy::~CasContainerStrategy()
 }
 
 void
-CasContainerStrategy::Initialize(const std::string_view ContainerBaseName, uint64_t Alignment, bool IsNewStore)
+CasContainerStrategy::Initialize(const std::string_view ContainerBaseName, uint32_t MaxBlockSize, uint64_t Alignment, bool IsNewStore)
 {
 	ZEN_ASSERT(IsPow2(Alignment));
 	ZEN_ASSERT(!m_IsInitialized);
+	ZEN_ASSERT(MaxBlockSize > 0);
 
 	m_ContainerBaseName = ContainerBaseName;
 	m_PayloadAlignment	= Alignment;
+	m_MaxBlockSize		= MaxBlockSize;
 
 	OpenContainer(IsNewStore);
 
@@ -79,11 +77,32 @@ CasContainerStrategy::InsertChunk(const void* ChunkData, size_t ChunkSize, const
 
 	// New entry
 
-	const uint64_t InsertOffset = m_CurrentInsertOffset;
-	m_SmallObjectFile.Write(ChunkData, ChunkSize, InsertOffset);
-	m_CurrentInsertOffset = AlignPositon(m_CurrentInsertOffset + ChunkSize, m_PayloadAlignment);
+	uint64_t CurrentBlockSize = m_CurrentBlock.lock()->FileSize();
+	if (CurrentBlockSize + m_CurrentInsertOffset > m_MaxBlockSize)
+	{
+		RwLock::ExclusiveLockScope __(m_LocationMapLock);
+		uint16_t				   NewBlockIndex = m_CurrentBlockIndex + 1;
+		while (m_OpenBlocks.contains(NewBlockIndex))
+		{
+			NewBlockIndex++;
+			if (NewBlockIndex == m_CurrentBlockIndex)
+			{
+				throw std::runtime_error(fmt::format("unable to allocate a new block in {}", m_ContainerBaseName));
+			}
+		}
+		m_CurrentBlockIndex					  = NewBlockIndex;
+		std::filesystem::path path			  = BuildUcasPath(m_Config.RootDirectory, m_ContainerBaseName, m_CurrentBlockIndex);
+		auto				  SmallObjectFile = std::make_shared<BasicFile>();
+		SmallObjectFile->Open(path, true);
+		m_OpenBlocks[m_CurrentBlockIndex] = SmallObjectFile;
+		m_CurrentBlock					  = SmallObjectFile;
+		m_CurrentInsertOffset			  = 0;
+	}
+	const uint32_t InsertOffset = m_CurrentInsertOffset;
+	m_CurrentBlock.lock()->Write(ChunkData, ChunkSize, InsertOffset);
+	m_CurrentInsertOffset = static_cast<uint32_t>(AlignPositon(InsertOffset + ChunkSize, m_PayloadAlignment));
 
-	const CasDiskLocation Location{InsertOffset, ChunkSize};
+	const CasDiskLocation Location{m_CurrentBlockIndex, InsertOffset, static_cast<uint32_t>(ChunkSize)};
 	CasDiskIndexEntry	  IndexEntry{.Key = ChunkHash, .Location = Location};
 
 	RwLock::ExclusiveLockScope __(m_LocationMapLock);
@@ -109,7 +128,10 @@ CasContainerStrategy::FindChunk(const IoHash& ChunkHash)
 	{
 		const CasDiskLocation& Location = KeyIt->second;
 
-		return IoBufferBuilder::MakeFromFileHandle(m_SmallObjectFile.Handle(), Location.GetOffset(), Location.GetSize());
+		if (auto BlockIt = m_OpenBlocks.find(Location.BlockIndex); BlockIt != m_OpenBlocks.end())
+		{
+			return IoBufferBuilder::MakeFromFileHandle(BlockIt->second->Handle(), Location.Offset, Location.Size);
+		}
 	}
 
 	// Not found
@@ -121,13 +143,7 @@ bool
 CasContainerStrategy::HaveChunk(const IoHash& ChunkHash)
 {
 	RwLock::SharedLockScope _(m_LocationMapLock);
-
-	if (auto KeyIt = m_LocationMap.find(ChunkHash); KeyIt != m_LocationMap.end())
-	{
-		return true;
-	}
-
-	return false;
+	return m_LocationMap.contains(ChunkHash);
 }
 
 void
@@ -146,18 +162,15 @@ CasContainerStrategy::FilterChunks(CasChunkSet& InOutChunks)
 void
 CasContainerStrategy::Flush()
 {
-	RwLock::SharedLockScope _(m_LocationMapLock);
+	RwLock::SharedLockScope _(m_InsertLock);
 	m_CasLog.Flush();
-	m_SmallObjectFile.Flush();
+	m_CurrentBlock.lock()->Flush();
 }
 
 void
 CasContainerStrategy::Scrub(ScrubContext& Ctx)
 {
-	const uint64_t WindowSize  = 4 * 1024 * 1024;
-	uint64_t	   WindowStart = 0;
-	uint64_t	   WindowEnd   = WindowSize;
-	const uint64_t FileSize	   = m_SmallObjectFile.FileSize();
+	const uint64_t WindowSize = 4 * 1024 * 1024;
 
 	std::vector<CasDiskIndexEntry> BigChunks;
 	std::vector<CasDiskIndexEntry> BadChunks;
@@ -171,51 +184,61 @@ CasContainerStrategy::Scrub(ScrubContext& Ctx)
 		IoBuffer ReadBuffer{WindowSize};
 		void*	 BufferBase = ReadBuffer.MutableData();
 
-		RwLock::SharedLockScope _(m_LocationMapLock);
+		RwLock::SharedLockScope _(m_InsertLock);  // TODO: Refactor so we don't have to keep m_InsertLock all the time?
+		RwLock::SharedLockScope __(m_LocationMapLock);
 
-		do
+		for (const auto& Block : m_OpenBlocks)
 		{
-			const uint64_t ChunkSize = Min(WindowSize, FileSize - WindowStart);
-			m_SmallObjectFile.Read(BufferBase, ChunkSize, WindowStart);
+			uint64_t	   WindowStart	   = 0;
+			uint64_t	   WindowEnd	   = WindowSize;
+			auto&		   SmallObjectFile = *Block.second;
+			const uint64_t FileSize		   = SmallObjectFile.FileSize();
 
-			for (auto& Entry : m_LocationMap)
+			do
 			{
-				const uint64_t EntryOffset = Entry.second.GetOffset();
+				const uint64_t ChunkSize = Min(WindowSize, FileSize - WindowStart);
+				SmallObjectFile.Read(BufferBase, ChunkSize, WindowStart);
 
-				if ((EntryOffset >= WindowStart) && (EntryOffset < WindowEnd))
+				for (auto& Entry : m_LocationMap)
 				{
-					const uint64_t EntryEnd = EntryOffset + Entry.second.GetSize();
+					const uint64_t EntryOffset = Entry.second.Offset;
 
-					if (EntryEnd >= WindowEnd)
+					if ((EntryOffset >= WindowStart) && (EntryOffset < WindowEnd))
 					{
-						BigChunks.push_back({.Key = Entry.first, .Location = Entry.second});
+						const uint64_t EntryEnd = EntryOffset + Entry.second.Size;
 
-						continue;
-					}
+						if (EntryEnd >= WindowEnd)
+						{
+							BigChunks.push_back({.Key = Entry.first, .Location = Entry.second});
 
-					const IoHash ComputedHash =
-						IoHash::HashBuffer(reinterpret_cast<uint8_t*>(BufferBase) + Entry.second.GetOffset() - WindowStart,
-										   Entry.second.GetSize());
+							continue;
+						}
 
-					if (Entry.first != ComputedHash)
-					{
-						// Hash mismatch
+						const IoHash ComputedHash =
+							IoHash::HashBuffer(reinterpret_cast<uint8_t*>(BufferBase) + Entry.second.Offset - WindowStart,
+											   Entry.second.Size);
 
-						BadChunks.push_back({.Key = Entry.first, .Location = Entry.second});
+						if (Entry.first != ComputedHash)
+						{
+							// Hash mismatch
+
+							BadChunks.push_back({.Key = Entry.first, .Location = Entry.second});
+						}
 					}
 				}
-			}
 
-			WindowStart += WindowSize;
-			WindowEnd += WindowSize;
-		} while (WindowStart < FileSize);
+				WindowStart += WindowSize;
+				WindowEnd += WindowSize;
+			} while (WindowStart < FileSize);
+		}
 
 		// Deal with large chunks
 
 		for (const CasDiskIndexEntry& Entry : BigChunks)
 		{
 			IoHashStream Hasher;
-			m_SmallObjectFile.StreamByteRange(Entry.Location.GetOffset(), Entry.Location.GetSize(), [&](const void* Data, uint64_t Size) {
+			auto&		 SmallObjectFile = *m_OpenBlocks[Entry.Location.BlockIndex];
+			SmallObjectFile.StreamByteRange(Entry.Location.Offset, Entry.Location.Size, [&](const void* Data, uint64_t Size) {
 				Hasher.Append(Data, Size);
 			});
 			IoHash ComputedHash = Hasher.GetHash();
@@ -258,33 +281,48 @@ CasContainerStrategy::CollectGarbage(GcContext& GcCtx)
 {
 	namespace fs = std::filesystem;
 
-	// Garbage collection will first remove any chunks that are flushed from the index.
-	// It then tries to compact the existing small object file, it does this by
-	// collecting all chunks that should be kept and sort them in position order.
-	// It then steps from chunk to chunk and checks if there is space to move the last
-	// chunk before the current chunk. It repeats this until it can't fit the last chunk
-	// or the last chunk is the current chunk.
-	// After this it check to see if there is space to move the current chunk closer to
-	// the preceeding chunk (or beginning of file if there is no preceeding chunk).
-	// It updates the new write position for any new chunks and rewrites the cas log
-	// to match the new content of the store.
+	// It collects all the blocks that we want to delete chunks from. For each such
+	// block we keep a list of chunks to retain.
 	//
-	// It currently grabs a full lock during the GC operation but the compacting is
-	// done gradually and can be stopped after each chunk if the GC operation needs to
-	// be time limited. This will leave holes in the small object file that will not
-	// be reclaimed unless a GC operation is executed again, but the state of the
-	// cas store is intact.
+	// It will first remove any chunks that are flushed from the m_LocationMap.
 	//
-	// It is also possible to more fine-grained locking of GC operation when moving
-	// blocks but that requires more work and additional checking if new blocks are
-	// added betwen each move of a block.
+	// It then checks to see if we want to purge any chunks that are in the currently
+	// active block. If so, we break off the current block and start on a new block,
+	// otherwise we just let the active block be.
+	//
+	// Next it will iterate over all blocks that we want to remove chunks from.
+	// If the block is empty after removal of chunks we mark the block as pending
+	// delete - we want to delete it as soon as there are no IoBuffers using the
+	// block file.
+	//
+	// If the block is non-empty we write out the chunks we want to keep to a new
+	// block file (creating new block files as needed).
+	//
+	// We update the index as we complete each new block file. This makes it possible
+	// to break the GC if we want to limit time for execution.
+	//
+	// GC can fairly parallell to regular operation - it will block while figuring
+	// out which chunks to remove and what blocks to rewrite but the actual
+	// reading and writing of data to new block files does not block regular operation.
+	//
+	// While moving blocks it will do a blocking operation and update the m_LocationMap
+	// after each new block is written and it will also block when figuring out the
+	// path to the next new block.
+
 	ZEN_INFO("collecting garbage from '{}'", m_Config.RootDirectory / m_ContainerBaseName);
 
+	std::unordered_map<uint64_t, size_t>									 BlockIndexToKeepChunksMap;
+	std::vector<std::unordered_map<IoHash, CasDiskLocation, IoHash::Hasher>> KeepChunks;
+	std::vector<IoHash>														 DeletedChunks;
+	std::unordered_set<uint16_t>											 BlocksToReWrite;
 	{
 		RwLock::ExclusiveLockScope _i(m_InsertLock);
 		RwLock::ExclusiveLockScope _l(m_LocationMapLock);
 
-		Flush();
+		m_CasLog.Flush();
+		m_CurrentBlock.lock()->Flush();
+
+		BlocksToReWrite.reserve(m_OpenBlocks.size());
 
 		if (m_LocationMap.empty())
 		{
@@ -297,21 +335,28 @@ CasContainerStrategy::CollectGarbage(GcContext& GcCtx)
 
 		std::vector<IoHash> TotalChunkHashes;
 		TotalChunkHashes.reserve(m_LocationMap.size());
-		for (auto& Entry : m_LocationMap)
+		for (const auto& Entry : m_LocationMap)
 		{
 			TotalChunkHashes.push_back(Entry.first);
+			if (BlockIndexToKeepChunksMap.contains(Entry.second.BlockIndex))
+			{
+				continue;
+			}
+			BlockIndexToKeepChunksMap[Entry.second.BlockIndex] = KeepChunks.size();
+			KeepChunks.resize(KeepChunks.size() + 1);
 		}
 
-		std::vector<IoHash> DeletedChunks;
-		std::vector<IoHash> ChunkHashes;  // Same sort order as ChunkLocations
-		ChunkHashes.reserve(m_LocationMap.size());
-
-		const bool CollectSmallObjects = GcCtx.IsDeletionMode() && GcCtx.CollectSmallObjects();
+		const bool PerformDelete = GcCtx.IsDeletionMode() && GcCtx.CollectSmallObjects();
 
+		uint64_t NewTotalSize = 0;
 		GcCtx.FilterCas(TotalChunkHashes, [&](const IoHash& ChunkHash, bool Keep) {
 			if (Keep)
 			{
-				ChunkHashes.push_back(ChunkHash);
+				auto		KeyIt		  = m_LocationMap.find(ChunkHash);
+				const auto& ChunkLocation = KeyIt->second;
+				auto&		ChunkMap	  = KeepChunks[BlockIndexToKeepChunksMap[ChunkLocation.BlockIndex]];
+				ChunkMap[ChunkHash]		  = ChunkLocation;
+				NewTotalSize += ChunkLocation.Size;
 			}
 			else
 			{
@@ -319,162 +364,172 @@ CasContainerStrategy::CollectGarbage(GcContext& GcCtx)
 			}
 		});
 
-		if (ChunkHashes.size() == TotalChunkCount)
-		{
-			ZEN_INFO("garbage collect DONE, scanned #{} {} chunks from '{}', nothing to delete",
-					 TotalChunkCount,
-					 NiceBytes(TotalSize),
-					 m_Config.RootDirectory / m_ContainerBaseName);
-			return;
-		}
-
-		const uint64_t ChunkCount = ChunkHashes.size();
-
-		std::sort(begin(ChunkHashes), end(ChunkHashes), [&](IoHash Lhs, IoHash Rhs) {
-			auto LhsKeyIt = m_LocationMap.find(Lhs);
-			auto RhsKeyIt = m_LocationMap.find(Rhs);
-			return LhsKeyIt->second.GetOffset() < RhsKeyIt->second.GetOffset();
-		});
-
-		uint64_t					 NewTotalSize = 0;
-		std::vector<CasDiskLocation> ChunkLocations;
-		ChunkLocations.reserve(ChunkHashes.size());
-		for (auto Entry : ChunkHashes)
-		{
-			auto		KeyIt		  = m_LocationMap.find(Entry);
-			const auto& ChunkLocation = KeyIt->second;
-			ChunkLocations.push_back(ChunkLocation);
-			NewTotalSize += ChunkLocation.GetSize();
-		}
-
-		if (!CollectSmallObjects)
+		if (!PerformDelete)
 		{
 			ZEN_INFO("garbage collect from '{}' DISABLED, found #{} {} chunks of total #{} {}",
 					 m_Config.RootDirectory / m_ContainerBaseName,
-					 TotalChunkCount - ChunkCount,
+					 DeletedChunks.size(),
 					 NiceBytes(TotalSize - NewTotalSize),
 					 TotalChunkCount,
 					 NiceBytes(TotalSize));
 			return;
 		}
 
-		for (auto ChunkHash : DeletedChunks)
+		for (const auto& ChunkHash : DeletedChunks)
 		{
-			auto		KeyIt			= m_LocationMap.find(ChunkHash);
-			const auto& ChunkLocation	= KeyIt->second;
-			uint64_t	NextChunkOffset = ChunkLocation.GetOffset() + ChunkLocation.GetSize();
+			auto		KeyIt		  = m_LocationMap.find(ChunkHash);
+			const auto& ChunkLocation = KeyIt->second;
+			BlocksToReWrite.insert(ChunkLocation.BlockIndex);
 			m_CasLog.Append({.Key = ChunkHash, .Location = ChunkLocation, .Flags = CasDiskIndexEntry::kTombstone});
 			m_LocationMap.erase(ChunkHash);
-			if (m_CurrentInsertOffset == NextChunkOffset)
+			m_TotalSize.fetch_sub(static_cast<uint64_t>(ChunkLocation.Size));
+		}
+
+		if (BlocksToReWrite.contains(m_CurrentBlockIndex))
+		{
+			uint16_t NewBlockIndex = m_CurrentBlockIndex + 1;
+			while (m_OpenBlocks.contains(NewBlockIndex))
 			{
-				m_CurrentInsertOffset = ChunkLocation.GetOffset();
+				NewBlockIndex++;
+				if (NewBlockIndex == m_CurrentBlockIndex)
+				{
+					ZEN_ERROR("unable to allocate a new block in {}, count limit {} exeeded",
+							  m_ContainerBaseName,
+							  std::numeric_limits<uint16_t>::max() + 1);
+					return;
+				}
 			}
-			m_TotalSize.fetch_sub(static_cast<uint64_t>(ChunkLocation.GetSize()));
+			m_CurrentBlockIndex					  = NewBlockIndex;
+			std::filesystem::path path			  = BuildUcasPath(m_Config.RootDirectory, m_ContainerBaseName, m_CurrentBlockIndex);
+			auto				  SmallObjectFile = std::make_shared<BasicFile>();
+			SmallObjectFile->Open(path, true);
+			m_OpenBlocks[m_CurrentBlockIndex] = SmallObjectFile;
+			m_CurrentBlock					  = SmallObjectFile;
+			m_CurrentInsertOffset			  = 0;
 		}
+	}
 
-		// We can break here if we only want to remove items without compacting of space
+	// Move all chunks in blocks that have chunks removed to new blocks
 
-		std::vector<IoHash> MovedChunks;
+	std::shared_ptr<BasicFile>					NewBlockFile;
+	uint64_t									WriteOffset	  = {};
+	uint16_t									NewBlockIndex = {};
+	std::unordered_map<IoHash, CasDiskLocation> MovedBlocks;
 
-		uint64_t WriteOffset{};
-		uint64_t ChunkIndex{};
-		while (ChunkIndex < ChunkHashes.size())
+	for (auto BlockIndex : BlocksToReWrite)
+	{
+		auto& ChunkMap = KeepChunks[BlockIndexToKeepChunksMap[BlockIndex]];
+		if (ChunkMap.empty())
 		{
-			IoHash		ChunkHash	  = ChunkHashes[ChunkIndex];
-			const auto& ChunkLocation = ChunkLocations[ChunkIndex];
-
-			uint64_t NextChunkOffset = AlignPositon(ChunkLocation.GetOffset() + ChunkLocation.GetSize(), m_PayloadAlignment);
+			// The block has no references to it, it should be removed as soon as no references is held on the file
+			// TODO: We currently don't know if someone is holding a IoBuffer for this block at this point!
+
+			// std::filesystem::path	   BlockPath = BuildUcasPath(m_Config.RootDirectory, m_ContainerBaseName, BlockIndex);
+			// RwLock::ExclusiveLockScope _i(m_InsertLock);
+			// auto BlockFile = m_OpenBlocks[BlockIndex];
+			// m_OpenBlocks.erase(BlockIndex);
+			// BlockFile->Close();
+			// fs::remove(BlockPath);
+			continue;
+		}
 
-			uint64_t FreeChunkSize = ChunkLocation.GetOffset() - WriteOffset;
+		std::shared_ptr<BasicFile> BlockFile;
+		{
+			RwLock::ExclusiveLockScope _i(m_InsertLock);
+			BlockFile = m_OpenBlocks[BlockIndex];
+		}
 
-			// TODO: We could keep some wiggle room here, only try to find the last keep block if there is a reasonable amount of space free
-			while (FreeChunkSize >= m_PayloadAlignment)
+		{
+			std::vector<uint8_t> Chunk;
+			for (auto& Entry : ChunkMap)
 			{
-				// We should move as many keep chunk at the end as we can possibly fit
-				uint64_t LastKeepChunkIndex = ChunkHashes.size() - 1;
-				if (LastKeepChunkIndex == ChunkIndex)
-				{
-					break;
-				}
+				const CasDiskLocation& ChunkLocation = Entry.second;
+				Chunk.resize(ChunkLocation.Size);
+				BlockFile->Read(Chunk.data(), Chunk.size(), ChunkLocation.Offset);
 
-				IoHash		LastChunkHash	  = ChunkHashes[LastKeepChunkIndex];
-				const auto& LastChunkLocation = ChunkLocations[LastKeepChunkIndex];
-				if (LastChunkLocation.GetSize() > FreeChunkSize)
+				if (!NewBlockFile || (WriteOffset + Chunk.size() > m_MaxBlockSize))
 				{
-					break;
-				}
-
-				// Move the last chunk to our write location
-				std::vector<uint8_t> Chunk;
-				Chunk.resize(LastChunkLocation.GetSize());
-				m_SmallObjectFile.Read(Chunk.data(), Chunk.size(), LastChunkLocation.GetOffset());
-				CasDiskLocation NewChunkLocation(WriteOffset, Chunk.size());
-				m_SmallObjectFile.Write(Chunk.data(), Chunk.size(), NewChunkLocation.GetOffset());
+					{
+						RwLock::ExclusiveLockScope _i(m_InsertLock);
+						if (NewBlockFile)
+						{
+							m_OpenBlocks[NewBlockIndex] = NewBlockFile;
+							RwLock::ExclusiveLockScope _l(m_LocationMapLock);
+							for (const auto& MovedEntry : MovedBlocks)
+							{
+								m_LocationMap[MovedEntry.first] = MovedEntry.second;
+								m_CasLog.Append({.Key = MovedEntry.first, .Location = MovedEntry.second});
+							}
+						}
+						NewBlockIndex = m_CurrentBlockIndex + 1;
+						while (m_OpenBlocks.contains(NewBlockIndex))
+						{
+							NewBlockIndex++;
+							if (NewBlockIndex == m_CurrentBlockIndex)
+							{
+								ZEN_ERROR("unable to allocate a new block in {}, count limit {} exeeded",
+										  m_ContainerBaseName,
+										  std::numeric_limits<uint16_t>::max() + 1);
+								return;
+							}
+						}
+						m_OpenBlocks[NewBlockIndex] = std::shared_ptr<BasicFile>();	 // Make sure nobody steals this slot
+					}
 
-				CasDiskIndexEntry IndexEntry{.Key = ChunkHash, .Location = NewChunkLocation};
-				m_CasLog.Append(IndexEntry);
-				m_LocationMap[LastChunkHash] = NewChunkLocation;
-				ChunkHashes.pop_back();
+					std::error_code Error;
+					DiskSpace		Space = DiskSpaceInfo(m_Config.RootDirectory, Error);
+					if (Error)
+					{
+						ZEN_ERROR("get disk space in {} FAILED, reason '{}'", m_ContainerBaseName, Error.message());
+						return;
+					}
 
-				WriteOffset	  = AlignPositon(WriteOffset + Chunk.size(), m_PayloadAlignment);
-				FreeChunkSize = ChunkLocation.GetOffset() - WriteOffset;
-				MovedChunks.push_back(LastChunkHash);
+					if (Space.Free < (m_MaxBlockSize * 2))	// Never let GC steal the last block space
+					{
+						ZEN_INFO("garbage collect from '{}' FAILED, required disk space {}, free {}",
+								 m_Config.RootDirectory / m_ContainerBaseName,
+								 m_MaxBlockSize * m_MaxBlockSize,
+								 NiceBytes(Space.Free));
+						RwLock::ExclusiveLockScope _i(m_InsertLock);
+						m_OpenBlocks.erase(NewBlockIndex);
+						return;
+					}
 
-				uint64_t LastChunkNextChunkOffset = AlignPositon(LastChunkLocation.GetOffset() + Chunk.size(), m_PayloadAlignment);
-				if (m_CurrentInsertOffset == LastChunkNextChunkOffset)
-				{
-					m_CurrentInsertOffset = LastChunkLocation.GetOffset();
+					std::filesystem::path NewBlockPath = BuildUcasPath(m_Config.RootDirectory, m_ContainerBaseName, NewBlockIndex);
+					NewBlockFile					   = std::make_shared<BasicFile>();
+					NewBlockFile->Open(NewBlockPath, true);
+					MovedBlocks.clear();
+					WriteOffset = 0;
 				}
-			}
 
-			// TODO: We could keep some wiggle room here, don't move chunk if we only move it a very small amount
-			if (FreeChunkSize > m_PayloadAlignment)
-			{
-				std::vector<uint8_t> Chunk;
-				Chunk.resize(ChunkLocation.GetSize());
-				m_SmallObjectFile.Read(Chunk.data(), Chunk.size(), ChunkLocation.GetOffset());
-				CasDiskLocation NewChunkLocation(WriteOffset, Chunk.size());
-				m_SmallObjectFile.Write(Chunk.data(), Chunk.size(), NewChunkLocation.GetOffset());
-
-				CasDiskIndexEntry IndexEntry{.Key = ChunkHash, .Location = NewChunkLocation};
-				m_CasLog.Append(IndexEntry);
-				m_LocationMap[ChunkHash] = NewChunkLocation;
-
-				MovedChunks.push_back(ChunkHash);
-				WriteOffset = AlignPositon(NewChunkLocation.GetOffset() + Chunk.size(), m_PayloadAlignment);
-			}
-			else
-			{
-				WriteOffset = NextChunkOffset;
+				NewBlockFile->Write(Chunk.data(), Chunk.size(), WriteOffset);
+				CasDiskLocation NewChunkLocation(NewBlockIndex, gsl::narrow<uint32_t>(WriteOffset), gsl::narrow<uint32_t>(Chunk.size()));
+				Entry.second			 = {.BlockIndex = NewBlockIndex,
+								.Offset		= gsl::narrow<uint32_t>(WriteOffset),
+								.Size		= gsl::narrow<uint32_t>(Chunk.size())};
+				MovedBlocks[Entry.first] = Entry.second;
+				WriteOffset				 = AlignPositon(WriteOffset + Chunk.size(), m_PayloadAlignment);
 			}
+			Chunk.clear();
 
-			// Update insert location if this is the last chunk in the file
-			if (m_CurrentInsertOffset == NextChunkOffset)
+			// Remap moved chunks to the new block file
+			RwLock::ExclusiveLockScope _i(m_InsertLock);
+			if (NewBlockFile)
 			{
-				m_CurrentInsertOffset = WriteOffset;
+				m_OpenBlocks[NewBlockIndex] = NewBlockFile;
+				RwLock::ExclusiveLockScope _l(m_LocationMapLock);
+				for (const auto& MovedEntry : MovedBlocks)
+				{
+					m_LocationMap[MovedEntry.first] = MovedEntry.second;
+					m_CasLog.Append({.Key = MovedEntry.first, .Location = MovedEntry.second});
+				}
 			}
-
-			// We can break here if we want to do incremental GC
-
-			ChunkIndex++;
-		}
-
-		if (ChunkCount == 0)
-		{
-			m_CurrentInsertOffset = 0;
 		}
+	}
 
-		GcCtx.DeletedCas(DeletedChunks);
+	GcCtx.DeletedCas(DeletedChunks);
 
-		uint64_t CurrentSize = m_SmallObjectFile.FileSize();
-		ZEN_INFO("garbage collection complete '{}', space {} to {}, moved {} and delete {} chunks",
-				 m_Config.RootDirectory / m_ContainerBaseName,
-				 NiceBytes(CurrentSize),
-				 NiceBytes(m_CurrentInsertOffset),
-				 MovedChunks.size(),
-				 DeletedChunks.size());
-		// TODO: Should we truncate the file or just keep the size of the file and reuse the space?
-	}
+	ZEN_INFO("garbage collection complete '{}', deleted {} chunks", m_Config.RootDirectory / m_ContainerBaseName, DeletedChunks.size());
 
 	MakeIndexSnapshot();
 }
@@ -592,16 +647,11 @@ CasContainerStrategy::MakeIndexSnapshot()
 void
 CasContainerStrategy::OpenContainer(bool IsNewStore)
 {
-	std::filesystem::path SobsPath = m_Config.RootDirectory / (m_ContainerBaseName + ".ucas");
-	std::filesystem::path SlogPath = m_Config.RootDirectory / (m_ContainerBaseName + ".ulog");
-
-	m_SmallObjectFile.Open(SobsPath, IsNewStore);
-	m_CasLog.Open(SlogPath, IsNewStore);
+	// TODO: Pick up old Cas store format so we can use it in our store
 
-	// TODO: should validate integrity of container files here
+	std::filesystem::path SlogPath = m_Config.RootDirectory / (m_ContainerBaseName + ".ulog");
 
-	m_CurrentInsertOffset = 0;
-	m_TotalSize			  = 0;
+	m_TotalSize = 0;
 
 	m_LocationMap.clear();
 
@@ -621,6 +671,7 @@ CasContainerStrategy::OpenContainer(bool IsNewStore)
 		SmallObjectIndex.Close();
 	}
 
+	m_CasLog.Open(SlogPath, IsNewStore);
 	m_CasLog.Replay([&](const CasDiskIndexEntry& Record) {
 		if (Record.Flags & CasDiskIndexEntry::kTombstone)
 		{
@@ -632,28 +683,104 @@ CasContainerStrategy::OpenContainer(bool IsNewStore)
 		}
 	});
 
-	uint64_t MaxFileOffset = 0;
+	std::unordered_set<uint16_t> ReferencedBlockIndexes;
 	for (const auto& Entry : m_LocationMap)
 	{
 		const auto& Location = Entry.second;
-		MaxFileOffset		 = std::max<uint64_t>(MaxFileOffset, Location.GetOffset() + Location.GetSize());
-		m_TotalSize.fetch_add(Location.GetSize());
+		m_TotalSize.fetch_add(Location.Size);
+		ReferencedBlockIndexes.insert(Location.BlockIndex);
+	}
+
+	uint32_t SmallestBlockSize = 0xffffffffu;
+	for (const std::filesystem::directory_entry& Entry : std::filesystem::directory_iterator(m_Config.RootDirectory))
+	{
+		if (Entry.is_regular_file())
+		{
+			// TODO: Clean up naming/storage structure so we don't have to do this complicated parsing to find our ucas files
+			if (Entry.path().extension() != ".ucas")
+			{
+				continue;
+			}
+			std::string FileName = Entry.path().stem().string();
+			if (!FileName.starts_with(m_ContainerBaseName))
+			{
+				continue;
+			}
+			if (IsNewStore)
+			{
+				std::filesystem::remove(Entry.path());
+				continue;
+			}
+			try
+			{
+				uint16_t BlockIndex = static_cast<uint16_t>(std::stoi(FileName.substr(m_ContainerBaseName.length() + 1)));
+				if (!ReferencedBlockIndexes.contains(BlockIndex))
+				{
+					// Clear out unused blocks
+					std::filesystem::remove(Entry.path());
+					continue;
+				}
+				auto SmallObjectFile = std::make_shared<BasicFile>();
+				SmallObjectFile->Open(Entry.path(), false);
+				m_OpenBlocks[BlockIndex] = SmallObjectFile;
+				if (SmallObjectFile->FileSize() < SmallestBlockSize)
+				{
+					m_CurrentBlockIndex = BlockIndex;
+					SmallestBlockSize	= gsl::narrow<std::uint32_t>(SmallObjectFile->FileSize());
+				}
+			}
+			catch (const std::invalid_argument&)
+			{
+				// Non-valid file, skip it (or should we remove it?)
+			}
+		}
+	}
+	if (m_OpenBlocks.empty())
+	{
+		std::filesystem::path path			  = BuildUcasPath(m_Config.RootDirectory, m_ContainerBaseName, m_CurrentBlockIndex);
+		auto				  SmallObjectFile = std::make_shared<BasicFile>();
+		SmallObjectFile->Open(path, true);
+		m_OpenBlocks[m_CurrentBlockIndex] = SmallObjectFile;
+		m_CurrentBlock					  = SmallObjectFile;
+		m_CurrentInsertOffset			  = 0;
+	}
+	else
+	{
+		m_CurrentBlock		  = m_OpenBlocks[m_CurrentBlockIndex];
+		m_CurrentInsertOffset = static_cast<uint32_t>(AlignPositon(m_CurrentBlock.lock()->FileSize(), m_PayloadAlignment));
 	}
 
-	m_CurrentInsertOffset = AlignPositon(MaxFileOffset, m_PayloadAlignment);
+	// TODO: should validate integrity of container files here
 }
 
 //////////////////////////////////////////////////////////////////////////
 
 #if ZEN_WITH_TESTS
 
+namespace {
+	static IoBuffer CreateChunk(uint64_t Size)
+	{
+		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);
+
+		return IoBufferBuilder::MakeCloneFromMemory(Values.data(), Values.size());
+	}
+}  // namespace
+
 TEST_CASE("cas.compact.gc")
 {
 	ScopedTemporaryDirectory TempDir;
 
 	CasStoreConfiguration CasConfig;
 	CasConfig.RootDirectory = TempDir.Path();
-
 	CreateDirectories(CasConfig.RootDirectory);
 
 	const int kIterationCount = 1000;
@@ -663,7 +790,7 @@ TEST_CASE("cas.compact.gc")
 	{
 		CasGc				 Gc;
 		CasContainerStrategy Cas(CasConfig, Gc);
-		Cas.Initialize("test", 16, true);
+		Cas.Initialize("test", 65536, 16, true);
 
 		for (int i = 0; i < kIterationCount; ++i)
 		{
@@ -697,7 +824,7 @@ TEST_CASE("cas.compact.gc")
 	{
 		CasGc				 Gc;
 		CasContainerStrategy Cas(CasConfig, Gc);
-		Cas.Initialize("test", 16, false);
+		Cas.Initialize("test", 65536, 16, false);
 
 		for (int i = 0; i < kIterationCount; ++i)
 		{
@@ -720,19 +847,6 @@ TEST_CASE("cas.compact.totalsize")
 	std::random_device rd;
 	std::mt19937	   g(rd());
 
-	const auto CreateChunk = [&](uint64_t Size) -> IoBuffer {
-		const size_t		  Count = static_cast<size_t>(Size / sizeof(uint32_t));
-		std::vector<uint32_t> Values;
-		Values.resize(Count);
-		for (size_t Idx = 0; Idx < Count; ++Idx)
-		{
-			Values[Idx] = static_cast<uint32_t>(Idx);
-		}
-		std::shuffle(Values.begin(), Values.end(), g);
-
-		return IoBufferBuilder::MakeCloneFromMemory(Values.data(), Values.size() * sizeof(uint32_t));
-	};
-
 	ScopedTemporaryDirectory TempDir;
 
 	CasStoreConfiguration CasConfig;
@@ -746,7 +860,7 @@ TEST_CASE("cas.compact.totalsize")
 	{
 		CasGc				 Gc;
 		CasContainerStrategy Cas(CasConfig, Gc);
-		Cas.Initialize("test", 16, true);
+		Cas.Initialize("test", 65536, 16, true);
 
 		for (int32_t Idx = 0; Idx < kChunkCount; ++Idx)
 		{
@@ -763,13 +877,385 @@ TEST_CASE("cas.compact.totalsize")
 	{
 		CasGc				 Gc;
 		CasContainerStrategy Cas(CasConfig, Gc);
-		Cas.Initialize("test", 16, false);
+		Cas.Initialize("test", 65536, 16, false);
 
 		const uint64_t TotalSize = Cas.StorageSize().DiskSize;
 		CHECK_EQ(kChunkSize * kChunkCount, TotalSize);
 	}
 }
 
+TEST_CASE("cas.gc.basic")
+{
+	ScopedTemporaryDirectory TempDir;
+
+	CasStoreConfiguration CasConfig;
+	CasConfig.RootDirectory = TempDir.Path();
+	CreateDirectories(CasConfig.RootDirectory);
+
+	CasGc				 Gc;
+	CasContainerStrategy Cas(CasConfig, Gc);
+	Cas.Initialize("cb", 65536, 1 << 4, true);
+
+	IoBuffer Chunk	   = CreateChunk(128);
+	IoHash	 ChunkHash = IoHash::HashBuffer(Chunk);
+
+	const auto InsertResult = Cas.InsertChunk(Chunk, ChunkHash);
+
+	GcContext GcCtx;
+	GcCtx.CollectSmallObjects(true);
+
+	Cas.CollectGarbage(GcCtx);
+
+	CHECK(!Cas.HaveChunk(ChunkHash));
+}
+
+TEST_CASE("cas.gc.compact")
+{
+	ScopedTemporaryDirectory TempDir;
+
+	CasStoreConfiguration CasConfig;
+	CasConfig.RootDirectory = TempDir.Path();
+	CreateDirectories(CasConfig.RootDirectory);
+
+	CasGc				 Gc;
+	CasContainerStrategy Cas(CasConfig, Gc);
+	Cas.Initialize("cb", 2048, 1 << 4, true);
+
+	uint64_t			  ChunkSizes[9] = {128, 541, 1023, 781, 218, 37, 4, 997, 5};
+	std::vector<IoBuffer> Chunks;
+	Chunks.reserve(9);
+	for (const auto& Size : ChunkSizes)
+	{
+		Chunks.push_back(CreateChunk(Size));
+	}
+
+	std::vector<IoHash> ChunkHashes;
+	ChunkHashes.reserve(9);
+	for (const auto& Chunk : Chunks)
+	{
+		ChunkHashes.push_back(IoHash::HashBuffer(Chunk.Data(), Chunk.Size()));
+	}
+
+	CHECK(Cas.InsertChunk(Chunks[0], ChunkHashes[0]).New);
+	CHECK(Cas.InsertChunk(Chunks[1], ChunkHashes[1]).New);
+	CHECK(Cas.InsertChunk(Chunks[2], ChunkHashes[2]).New);
+	CHECK(Cas.InsertChunk(Chunks[3], ChunkHashes[3]).New);
+	CHECK(Cas.InsertChunk(Chunks[4], ChunkHashes[4]).New);
+	CHECK(Cas.InsertChunk(Chunks[5], ChunkHashes[5]).New);
+	CHECK(Cas.InsertChunk(Chunks[6], ChunkHashes[6]).New);
+	CHECK(Cas.InsertChunk(Chunks[7], ChunkHashes[7]).New);
+	CHECK(Cas.InsertChunk(Chunks[8], ChunkHashes[8]).New);
+
+	CHECK(Cas.HaveChunk(ChunkHashes[0]));
+	CHECK(Cas.HaveChunk(ChunkHashes[1]));
+	CHECK(Cas.HaveChunk(ChunkHashes[2]));
+	CHECK(Cas.HaveChunk(ChunkHashes[3]));
+	CHECK(Cas.HaveChunk(ChunkHashes[4]));
+	CHECK(Cas.HaveChunk(ChunkHashes[5]));
+	CHECK(Cas.HaveChunk(ChunkHashes[6]));
+	CHECK(Cas.HaveChunk(ChunkHashes[7]));
+	CHECK(Cas.HaveChunk(ChunkHashes[8]));
+
+	auto InitialSize = Cas.StorageSize().DiskSize;
+
+	// Keep first and last
+	{
+		GcContext GcCtx;
+		GcCtx.CollectSmallObjects(true);
+
+		std::vector<IoHash> KeepChunks;
+		KeepChunks.push_back(ChunkHashes[0]);
+		KeepChunks.push_back(ChunkHashes[8]);
+		GcCtx.ContributeCas(KeepChunks);
+
+		Cas.CollectGarbage(GcCtx);
+
+		CHECK(Cas.HaveChunk(ChunkHashes[0]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[1]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[2]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[3]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[4]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[5]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[6]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[7]));
+		CHECK(Cas.HaveChunk(ChunkHashes[8]));
+
+		CHECK(ChunkHashes[0] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[0])));
+		CHECK(ChunkHashes[8] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[8])));
+	}
+
+	Cas.InsertChunk(Chunks[1], ChunkHashes[1]);
+	Cas.InsertChunk(Chunks[2], ChunkHashes[2]);
+	Cas.InsertChunk(Chunks[3], ChunkHashes[3]);
+	Cas.InsertChunk(Chunks[4], ChunkHashes[4]);
+	Cas.InsertChunk(Chunks[5], ChunkHashes[5]);
+	Cas.InsertChunk(Chunks[6], ChunkHashes[6]);
+	Cas.InsertChunk(Chunks[7], ChunkHashes[7]);
+
+	// Keep last
+	{
+		GcContext GcCtx;
+		GcCtx.CollectSmallObjects(true);
+		std::vector<IoHash> KeepChunks;
+		KeepChunks.push_back(ChunkHashes[8]);
+		GcCtx.ContributeCas(KeepChunks);
+
+		Cas.CollectGarbage(GcCtx);
+
+		CHECK(!Cas.HaveChunk(ChunkHashes[0]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[1]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[2]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[3]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[4]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[5]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[6]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[7]));
+		CHECK(Cas.HaveChunk(ChunkHashes[8]));
+
+		CHECK(ChunkHashes[8] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[8])));
+
+		Cas.InsertChunk(Chunks[1], ChunkHashes[1]);
+		Cas.InsertChunk(Chunks[2], ChunkHashes[2]);
+		Cas.InsertChunk(Chunks[3], ChunkHashes[3]);
+		Cas.InsertChunk(Chunks[4], ChunkHashes[4]);
+		Cas.InsertChunk(Chunks[5], ChunkHashes[5]);
+		Cas.InsertChunk(Chunks[6], ChunkHashes[6]);
+		Cas.InsertChunk(Chunks[7], ChunkHashes[7]);
+	}
+
+	// Keep mixed
+	{
+		GcContext GcCtx;
+		GcCtx.CollectSmallObjects(true);
+		std::vector<IoHash> KeepChunks;
+		KeepChunks.push_back(ChunkHashes[1]);
+		KeepChunks.push_back(ChunkHashes[4]);
+		KeepChunks.push_back(ChunkHashes[7]);
+		GcCtx.ContributeCas(KeepChunks);
+
+		Cas.CollectGarbage(GcCtx);
+
+		CHECK(!Cas.HaveChunk(ChunkHashes[0]));
+		CHECK(Cas.HaveChunk(ChunkHashes[1]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[2]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[3]));
+		CHECK(Cas.HaveChunk(ChunkHashes[4]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[5]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[6]));
+		CHECK(Cas.HaveChunk(ChunkHashes[7]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[8]));
+
+		CHECK(ChunkHashes[1] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[1])));
+		CHECK(ChunkHashes[4] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[4])));
+		CHECK(ChunkHashes[7] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[7])));
+
+		Cas.InsertChunk(Chunks[0], ChunkHashes[0]);
+		Cas.InsertChunk(Chunks[2], ChunkHashes[2]);
+		Cas.InsertChunk(Chunks[3], ChunkHashes[3]);
+		Cas.InsertChunk(Chunks[5], ChunkHashes[5]);
+		Cas.InsertChunk(Chunks[6], ChunkHashes[6]);
+		Cas.InsertChunk(Chunks[8], ChunkHashes[8]);
+	}
+
+	// Keep multiple at end
+	{
+		GcContext GcCtx;
+		GcCtx.CollectSmallObjects(true);
+		std::vector<IoHash> KeepChunks;
+		KeepChunks.push_back(ChunkHashes[6]);
+		KeepChunks.push_back(ChunkHashes[7]);
+		KeepChunks.push_back(ChunkHashes[8]);
+		GcCtx.ContributeCas(KeepChunks);
+
+		Cas.CollectGarbage(GcCtx);
+
+		CHECK(!Cas.HaveChunk(ChunkHashes[0]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[1]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[2]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[3]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[4]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[5]));
+		CHECK(Cas.HaveChunk(ChunkHashes[6]));
+		CHECK(Cas.HaveChunk(ChunkHashes[7]));
+		CHECK(Cas.HaveChunk(ChunkHashes[8]));
+
+		CHECK(ChunkHashes[6] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[6])));
+		CHECK(ChunkHashes[7] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[7])));
+		CHECK(ChunkHashes[8] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[8])));
+
+		Cas.InsertChunk(Chunks[0], ChunkHashes[0]);
+		Cas.InsertChunk(Chunks[1], ChunkHashes[1]);
+		Cas.InsertChunk(Chunks[2], ChunkHashes[2]);
+		Cas.InsertChunk(Chunks[3], ChunkHashes[3]);
+		Cas.InsertChunk(Chunks[4], ChunkHashes[4]);
+		Cas.InsertChunk(Chunks[5], ChunkHashes[5]);
+	}
+
+	// Keep every other
+	{
+		GcContext GcCtx;
+		GcCtx.CollectSmallObjects(true);
+		std::vector<IoHash> KeepChunks;
+		KeepChunks.push_back(ChunkHashes[0]);
+		KeepChunks.push_back(ChunkHashes[2]);
+		KeepChunks.push_back(ChunkHashes[4]);
+		KeepChunks.push_back(ChunkHashes[6]);
+		KeepChunks.push_back(ChunkHashes[8]);
+		GcCtx.ContributeCas(KeepChunks);
+
+		Cas.CollectGarbage(GcCtx);
+
+		CHECK(Cas.HaveChunk(ChunkHashes[0]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[1]));
+		CHECK(Cas.HaveChunk(ChunkHashes[2]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[3]));
+		CHECK(Cas.HaveChunk(ChunkHashes[4]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[5]));
+		CHECK(Cas.HaveChunk(ChunkHashes[6]));
+		CHECK(!Cas.HaveChunk(ChunkHashes[7]));
+		CHECK(Cas.HaveChunk(ChunkHashes[8]));
+
+		CHECK(ChunkHashes[0] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[0])));
+		CHECK(ChunkHashes[2] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[2])));
+		CHECK(ChunkHashes[4] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[4])));
+		CHECK(ChunkHashes[6] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[6])));
+		CHECK(ChunkHashes[8] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[8])));
+
+		Cas.InsertChunk(Chunks[1], ChunkHashes[1]);
+		Cas.InsertChunk(Chunks[3], ChunkHashes[3]);
+		Cas.InsertChunk(Chunks[5], ChunkHashes[5]);
+		Cas.InsertChunk(Chunks[7], ChunkHashes[7]);
+	}
+
+	// Verify that we nicely appended blocks even after all GC operations
+	CHECK(ChunkHashes[0] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[0])));
+	CHECK(ChunkHashes[1] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[1])));
+	CHECK(ChunkHashes[2] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[2])));
+	CHECK(ChunkHashes[3] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[3])));
+	CHECK(ChunkHashes[4] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[4])));
+	CHECK(ChunkHashes[5] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[5])));
+	CHECK(ChunkHashes[6] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[6])));
+	CHECK(ChunkHashes[7] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[7])));
+	CHECK(ChunkHashes[8] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[8])));
+
+	auto FinalSize = Cas.StorageSize().DiskSize;
+	CHECK(InitialSize == FinalSize);
+}
+
+TEST_CASE("cas.gc.deleteblockonopen")
+{
+	ScopedTemporaryDirectory TempDir;
+
+	uint64_t			  ChunkSizes[20] = {128, 541, 311, 181, 218, 37, 4, 397, 5, 92, 551, 721, 31, 92, 16, 99, 131, 41, 541, 84};
+	std::vector<IoBuffer> Chunks;
+	Chunks.reserve(20);
+	for (const auto& Size : ChunkSizes)
+	{
+		Chunks.push_back(CreateChunk(Size));
+	}
+
+	std::vector<IoHash> ChunkHashes;
+	ChunkHashes.reserve(20);
+	for (const auto& Chunk : Chunks)
+	{
+		ChunkHashes.push_back(IoHash::HashBuffer(Chunk.Data(), Chunk.Size()));
+	}
+
+	CasStoreConfiguration CasConfig;
+	CasConfig.RootDirectory = TempDir.Path();
+	CreateDirectories(CasConfig.RootDirectory);
+	{
+		CasGc				 Gc;
+		CasContainerStrategy Cas(CasConfig, Gc);
+		Cas.Initialize("test", 1024, 16, true);
+
+		for (size_t i = 0; i < 20; i++)
+		{
+			CHECK(Cas.InsertChunk(Chunks[i], ChunkHashes[i]).New);
+		}
+
+		// GC every other block
+		{
+			GcContext GcCtx;
+			GcCtx.CollectSmallObjects(true);
+			std::vector<IoHash> KeepChunks;
+			for (size_t i = 0; i < 20; i += 2)
+			{
+				KeepChunks.push_back(ChunkHashes[i]);
+			}
+			GcCtx.ContributeCas(KeepChunks);
+
+			Cas.CollectGarbage(GcCtx);
+
+			for (size_t i = 0; i < 20; i += 2)
+			{
+				CHECK(Cas.HaveChunk(ChunkHashes[i]));
+				CHECK(!Cas.HaveChunk(ChunkHashes[i + 1]));
+				CHECK(ChunkHashes[i] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[i])));
+			}
+		}
+	}
+	{
+		// Re-open
+		CasGc				 Gc;
+		CasContainerStrategy Cas(CasConfig, Gc);
+		Cas.Initialize("test", 1024, 16, false);
+
+		for (size_t i = 0; i < 20; i += 2)
+		{
+			CHECK(Cas.HaveChunk(ChunkHashes[i]));
+			CHECK(!Cas.HaveChunk(ChunkHashes[i + 1]));
+			CHECK(ChunkHashes[i] == IoHash::HashBuffer(Cas.FindChunk(ChunkHashes[i])));
+		}
+	}
+}
+
+TEST_CASE("cas.gc.handleopeniobuffer")
+{
+	ScopedTemporaryDirectory TempDir;
+
+	uint64_t			  ChunkSizes[20] = {128, 541, 311, 181, 218, 37, 4, 397, 5, 92, 551, 721, 31, 92, 16, 99, 131, 41, 541, 84};
+	std::vector<IoBuffer> Chunks;
+	Chunks.reserve(20);
+	for (const auto& Size : ChunkSizes)
+	{
+		Chunks.push_back(CreateChunk(Size));
+	}
+
+	std::vector<IoHash> ChunkHashes;
+	ChunkHashes.reserve(20);
+	for (const auto& Chunk : Chunks)
+	{
+		ChunkHashes.push_back(IoHash::HashBuffer(Chunk.Data(), Chunk.Size()));
+	}
+
+	CasStoreConfiguration CasConfig;
+	CasConfig.RootDirectory = TempDir.Path();
+	CreateDirectories(CasConfig.RootDirectory);
+
+	CasGc				 Gc;
+	CasContainerStrategy Cas(CasConfig, Gc);
+	Cas.Initialize("test", 1024, 16, true);
+
+	for (size_t i = 0; i < 20; i++)
+	{
+		CHECK(Cas.InsertChunk(Chunks[i], ChunkHashes[i]).New);
+	}
+
+	auto RetainChunk = Cas.FindChunk(ChunkHashes[5]);
+
+	// GC everything
+	GcContext GcCtx;
+	GcCtx.CollectSmallObjects(true);
+	Cas.CollectGarbage(GcCtx);
+
+	for (size_t i = 0; i < 20; i++)
+	{
+		CHECK(!Cas.HaveChunk(ChunkHashes[i]));
+	}
+
+	CHECK(ChunkHashes[5] == IoHash::HashBuffer(RetainChunk));
+}
 #endif
 
 void