diff --git a/src/blobstore/implementations/onblocks/BlobOnBlocks.cpp b/src/blobstore/implementations/onblocks/BlobOnBlocks.cpp
index e0e282c2..51d04b04 100644
--- a/src/blobstore/implementations/onblocks/BlobOnBlocks.cpp
+++ b/src/blobstore/implementations/onblocks/BlobOnBlocks.cpp
@@ -2,6 +2,7 @@
 #include "BlobOnBlocks.h"
 
 #include "datanodestore/DataLeafNode.h"
+#include "datanodestore/DataNodeStore.h"
 #include "utils/Math.h"
 #include <cmath>
 #include <cpp-utils/assert/assert.h>
@@ -127,7 +128,14 @@ void BlobOnBlocks::write(const void *source, uint64_t offset, uint64_t count) {
   auto onExistingLeaf = [source, offset, count] (uint64_t indexOfFirstLeafByte, LeafHandle leaf, uint32_t leafDataOffset, uint32_t leafDataSize) {
       ASSERT(indexOfFirstLeafByte+leafDataOffset>=offset && indexOfFirstLeafByte-offset+leafDataOffset <= count && indexOfFirstLeafByte-offset+leafDataOffset+leafDataSize <= count, "Reading from source out of bounds");
       //TODO Simplify formula, make it easier to understand
-      leaf.node()->write((uint8_t*)source + indexOfFirstLeafByte - offset + leafDataOffset, leafDataOffset, leafDataSize);
+      if (leafDataOffset == 0 && leafDataSize == leaf.nodeStore()->layout().maxBytesPerLeaf()) {
+        Data leafData(leafDataSize);
+        std::memcpy(leafData.data(), (uint8_t*)source + indexOfFirstLeafByte - offset, leafDataSize);
+        leaf.nodeStore()->overwriteLeaf(leaf.key(), std::move(leafData));
+      } else {
+        leaf.node()->write((uint8_t *) source + indexOfFirstLeafByte - offset + leafDataOffset, leafDataOffset,
+                           leafDataSize);
+      }
   };
   auto onCreateLeaf = [source, offset, count] (uint64_t beginByte, uint32_t numBytes) -> Data {
       ASSERT(beginByte >= offset && beginByte-offset <= count && beginByte-offset+numBytes <= count, "Reading from source out of bounds");
diff --git a/src/blobstore/implementations/onblocks/datanodestore/DataLeafNode.cpp b/src/blobstore/implementations/onblocks/datanodestore/DataLeafNode.cpp
index f1d7ab13..7f8b9335 100644
--- a/src/blobstore/implementations/onblocks/datanodestore/DataLeafNode.cpp
+++ b/src/blobstore/implementations/onblocks/datanodestore/DataLeafNode.cpp
@@ -31,6 +31,12 @@ unique_ref<DataLeafNode> DataLeafNode::CreateNewNode(BlockStore *blockStore, con
   return make_unique_ref<DataLeafNode>(DataNodeView::create(blockStore, layout, DataNode::FORMAT_VERSION_HEADER, 0, size, std::move(data)));
 }
 
+unique_ref<DataLeafNode> DataLeafNode::OverwriteNode(BlockStore *blockStore, const DataNodeLayout &layout, const Key &key, Data data) {
+  ASSERT(data.size() == layout.maxBytesPerLeaf(), "Data passed in is too large for one leaf.");
+  uint32_t size = data.size();
+  return make_unique_ref<DataLeafNode>(DataNodeView::overwrite(blockStore, layout, DataNode::FORMAT_VERSION_HEADER, 0, size, key, std::move(data)));
+}
+
 void DataLeafNode::read(void *target, uint64_t offset, uint64_t size) const {
   ASSERT(offset <= node().Size() && offset + size <= node().Size(), "Read out of valid area"); // Also check offset, because the addition could lead to overflows
   std::memcpy(target, (uint8_t*)node().data() + offset, size);
diff --git a/src/blobstore/implementations/onblocks/datanodestore/DataLeafNode.h b/src/blobstore/implementations/onblocks/datanodestore/DataLeafNode.h
index f509a850..3839a7ed 100644
--- a/src/blobstore/implementations/onblocks/datanodestore/DataLeafNode.h
+++ b/src/blobstore/implementations/onblocks/datanodestore/DataLeafNode.h
@@ -11,8 +11,8 @@ class DataInnerNode;
 
 class DataLeafNode final: public DataNode {
 public:
-  //static cpputils::unique_ref<DataLeafNode> InitializeNewNode(cpputils::unique_ref<blockstore::Block> block);
   static cpputils::unique_ref<DataLeafNode> CreateNewNode(blockstore::BlockStore *blockStore, const DataNodeLayout &layout, cpputils::Data data);
+  static cpputils::unique_ref<DataLeafNode> OverwriteNode(blockstore::BlockStore *blockStore, const DataNodeLayout &layout, const blockstore::Key &key, cpputils::Data data);
 
   DataLeafNode(DataNodeView block);
   ~DataLeafNode();
diff --git a/src/blobstore/implementations/onblocks/datanodestore/DataNodeStore.cpp b/src/blobstore/implementations/onblocks/datanodestore/DataNodeStore.cpp
index ae821823..42ab53c9 100644
--- a/src/blobstore/implementations/onblocks/datanodestore/DataNodeStore.cpp
+++ b/src/blobstore/implementations/onblocks/datanodestore/DataNodeStore.cpp
@@ -50,6 +50,10 @@ unique_ref<DataLeafNode> DataNodeStore::createNewLeafNode(Data data) {
   return DataLeafNode::CreateNewNode(_blockstore.get(), _layout, std::move(data));
 }
 
+unique_ref<DataLeafNode> DataNodeStore::overwriteLeaf(const Key &key, Data data) {
+  return DataLeafNode::OverwriteNode(_blockstore.get(), _layout, key, std::move(data));
+}
+
 optional<unique_ref<DataNode>> DataNodeStore::load(const Key &key) {
   auto block = _blockstore->load(key);
   if (block == none) {
diff --git a/src/blobstore/implementations/onblocks/datanodestore/DataNodeStore.h b/src/blobstore/implementations/onblocks/datanodestore/DataNodeStore.h
index 351bdf23..37d27f4d 100644
--- a/src/blobstore/implementations/onblocks/datanodestore/DataNodeStore.h
+++ b/src/blobstore/implementations/onblocks/datanodestore/DataNodeStore.h
@@ -38,6 +38,8 @@ public:
 
   cpputils::unique_ref<DataNode> overwriteNodeWith(cpputils::unique_ref<DataNode> target, const DataNode &source);
 
+  cpputils::unique_ref<DataLeafNode> overwriteLeaf(const blockstore::Key &key, cpputils::Data data);
+
   void remove(cpputils::unique_ref<DataNode> node);
   void remove(const blockstore::Key &key);
   void removeSubtree(uint8_t depth, const blockstore::Key &key);
diff --git a/src/blobstore/implementations/onblocks/datanodestore/DataNodeView.h b/src/blobstore/implementations/onblocks/datanodestore/DataNodeView.h
index 57f63f76..2b55e7e7 100644
--- a/src/blobstore/implementations/onblocks/datanodestore/DataNodeView.h
+++ b/src/blobstore/implementations/onblocks/datanodestore/DataNodeView.h
@@ -81,6 +81,13 @@ public:
     return DataNodeView(std::move(block));
   }
 
+  static DataNodeView overwrite(blockstore::BlockStore *blockStore, const DataNodeLayout &layout, uint16_t formatVersion, uint8_t depth, uint32_t size, const blockstore::Key &key, cpputils::Data data) {
+    ASSERT(data.size() <= layout.datasizeBytes(), "Data is too large for node");
+    cpputils::Data serialized = _serialize(layout, formatVersion, depth, size, std::move(data));
+    auto block = blockStore->overwrite(key, std::move(serialized));
+    return DataNodeView(std::move(block));
+  }
+
   DataNodeView(DataNodeView &&rhs) = default;
 
   uint16_t FormatVersion() const {
diff --git a/src/blobstore/implementations/onblocks/datatreestore/LeafHandle.h b/src/blobstore/implementations/onblocks/datatreestore/LeafHandle.h
index 42821c15..aba8c67f 100644
--- a/src/blobstore/implementations/onblocks/datatreestore/LeafHandle.h
+++ b/src/blobstore/implementations/onblocks/datatreestore/LeafHandle.h
@@ -26,6 +26,10 @@ namespace blobstore {
 
                 datanodestore::DataLeafNode *node();
 
+                datanodestore::DataNodeStore *nodeStore() {
+                    return _nodeStore;
+                }
+
             private:
                 datanodestore::DataNodeStore *_nodeStore;
                 blockstore::Key _key;
diff --git a/src/blockstore/implementations/caching/CachingBlockStore.cpp b/src/blockstore/implementations/caching/CachingBlockStore.cpp
index df35bd59..1f85e7d6 100644
--- a/src/blockstore/implementations/caching/CachingBlockStore.cpp
+++ b/src/blockstore/implementations/caching/CachingBlockStore.cpp
@@ -49,6 +49,20 @@ optional<unique_ref<Block>> CachingBlockStore::load(const Key &key) {
   }
 }
 
+unique_ref<Block> CachingBlockStore::overwrite(const Key &key, cpputils::Data data) {
+  optional<unique_ref<Block>> optBlock = _cache.pop(key);
+  if (optBlock != none) {
+    if ((*optBlock)->size() != data.size()) {
+      (*optBlock)->resize(data.size());
+    }
+    (*optBlock)->write(data.data(), 0, data.size());
+    return make_unique_ref<CachedBlock>(std::move(*optBlock), this);
+  } else {
+    auto block = _baseBlockStore->overwrite(key, std::move(data));
+    return make_unique_ref<CachedBlock>(std::move(block), this);
+  }
+}
+
 void CachingBlockStore::remove(cpputils::unique_ref<Block> block) {
   auto cached_block = dynamic_pointer_move<CachedBlock>(block);
   ASSERT(cached_block != none, "Passed block is not a CachedBlock");
diff --git a/src/blockstore/implementations/caching/CachingBlockStore.h b/src/blockstore/implementations/caching/CachingBlockStore.h
index 6596fdea..99dde3d9 100644
--- a/src/blockstore/implementations/caching/CachingBlockStore.h
+++ b/src/blockstore/implementations/caching/CachingBlockStore.h
@@ -18,6 +18,7 @@ public:
 
   Key createKey() override;
   boost::optional<cpputils::unique_ref<Block>> tryCreate(const Key &key, cpputils::Data data) override;
+  cpputils::unique_ref<Block> overwrite(const Key &key, cpputils::Data data) override;
   boost::optional<cpputils::unique_ref<Block>> load(const Key &key) override;
   void remove(const Key &key) override;
   void remove(cpputils::unique_ref<Block> block) override;
diff --git a/src/blockstore/implementations/compressing/CompressedBlock.h b/src/blockstore/implementations/compressing/CompressedBlock.h
index 35f07340..88b6c55b 100644
--- a/src/blockstore/implementations/compressing/CompressedBlock.h
+++ b/src/blockstore/implementations/compressing/CompressedBlock.h
@@ -17,6 +17,7 @@ template<class Compressor>
 class CompressedBlock final: public Block {
 public:
   static boost::optional<cpputils::unique_ref<CompressedBlock>> TryCreateNew(BlockStore *baseBlockStore, const Key &key, cpputils::Data decompressedData);
+  static cpputils::unique_ref<CompressedBlock> Overwrite(BlockStore *baseBlockStore, const Key &key, cpputils::Data decompressedData);
   static cpputils::unique_ref<CompressedBlock> Decompress(cpputils::unique_ref<Block> baseBlock);
 
   CompressedBlock(cpputils::unique_ref<Block> baseBlock, cpputils::Data decompressedData);
@@ -55,6 +56,14 @@ boost::optional<cpputils::unique_ref<CompressedBlock<Compressor>>> CompressedBlo
   return cpputils::make_unique_ref<CompressedBlock<Compressor>>(std::move(*baseBlock), std::move(decompressedData));
 }
 
+template<class Compressor>
+cpputils::unique_ref<CompressedBlock<Compressor>> CompressedBlock<Compressor>::Overwrite(BlockStore *baseBlockStore, const Key &key, cpputils::Data decompressedData) {
+  cpputils::Data compressed = Compressor::Compress(decompressedData);
+  auto baseBlock = baseBlockStore->overwrite(key, std::move(compressed));
+
+  return cpputils::make_unique_ref<CompressedBlock<Compressor>>(std::move(baseBlock), std::move(decompressedData));
+}
+
 template<class Compressor>
 cpputils::unique_ref<CompressedBlock<Compressor>> CompressedBlock<Compressor>::Decompress(cpputils::unique_ref<Block> baseBlock) {
   cpputils::Data decompressed = Compressor::Decompress((byte*)baseBlock->data(), baseBlock->size());
diff --git a/src/blockstore/implementations/compressing/CompressingBlockStore.h b/src/blockstore/implementations/compressing/CompressingBlockStore.h
index 8a877e6e..ef187b31 100644
--- a/src/blockstore/implementations/compressing/CompressingBlockStore.h
+++ b/src/blockstore/implementations/compressing/CompressingBlockStore.h
@@ -17,6 +17,7 @@ public:
     Key createKey() override;
     boost::optional<cpputils::unique_ref<Block>> tryCreate(const Key &key, cpputils::Data data) override;
     boost::optional<cpputils::unique_ref<Block>> load(const Key &key) override;
+    cpputils::unique_ref<Block> overwrite(const blockstore::Key &key, cpputils::Data data) override;
     void remove(const Key &key) override;
     uint64_t numBlocks() const override;
     uint64_t estimateNumFreeBytes() const override;
@@ -52,6 +53,11 @@ boost::optional<cpputils::unique_ref<Block>> CompressingBlockStore<Compressor>::
     return cpputils::unique_ref<Block>(std::move(*result));
 }
 
+template<class Compressor>
+cpputils::unique_ref<Block> CompressingBlockStore<Compressor>::overwrite(const blockstore::Key &key, cpputils::Data data) {
+    return CompressedBlock<Compressor>::Overwrite(_baseBlockStore.get(), key, std::move(data));
+}
+
 template<class Compressor>
 boost::optional<cpputils::unique_ref<Block>> CompressingBlockStore<Compressor>::load(const Key &key) {
     auto loaded = _baseBlockStore->load(key);
diff --git a/src/blockstore/implementations/encrypted/EncryptedBlock.h b/src/blockstore/implementations/encrypted/EncryptedBlock.h
index 47632a1e..ea3e173a 100644
--- a/src/blockstore/implementations/encrypted/EncryptedBlock.h
+++ b/src/blockstore/implementations/encrypted/EncryptedBlock.h
@@ -29,6 +29,7 @@ class EncryptedBlock final: public Block {
 public:
   BOOST_CONCEPT_ASSERT((cpputils::CipherConcept<Cipher>));
   static boost::optional<cpputils::unique_ref<EncryptedBlock>> TryCreateNew(BlockStore *baseBlockStore, const Key &key, cpputils::Data data, const typename Cipher::EncryptionKey &encKey);
+  static cpputils::unique_ref<EncryptedBlock> Overwrite(BlockStore *baseBlockStore, const Key &key, cpputils::Data data, const typename Cipher::EncryptionKey &encKey);
   static boost::optional<cpputils::unique_ref<EncryptedBlock>> TryDecrypt(cpputils::unique_ref<Block> baseBlock, const typename Cipher::EncryptionKey &key);
 
   static uint64_t blockSizeFromPhysicalBlockSize(uint64_t blockSize);
@@ -91,6 +92,17 @@ boost::optional<cpputils::unique_ref<EncryptedBlock<Cipher>>> EncryptedBlock<Cip
   return cpputils::make_unique_ref<EncryptedBlock>(std::move(*baseBlock), encKey, std::move(plaintextWithHeader));
 }
 
+template<class Cipher>
+cpputils::unique_ref<EncryptedBlock<Cipher>> EncryptedBlock<Cipher>::Overwrite(BlockStore *baseBlockStore, const Key &key, cpputils::Data data, const typename Cipher::EncryptionKey &encKey) {
+  //TODO Is it possible to avoid copying the whole plaintext data into plaintextWithHeader? Maybe an encrypt() object that has an .addData() function and concatenates all data for encryption? Maybe Crypto++ offers this functionality already.
+  cpputils::Data plaintextWithHeader = _prependKeyHeaderToData(key, std::move(data));
+  cpputils::Data encrypted = Cipher::encrypt((byte*)plaintextWithHeader.data(), plaintextWithHeader.size(), encKey);
+  //TODO Avoid copying the whole encrypted block into a encryptedWithFormatHeader by creating a Data object with full size and then giving it as an encryption target to Cipher::encrypt()
+  cpputils::Data encryptedWithFormatHeader = _prependFormatHeader(std::move(encrypted));
+  auto baseBlock = baseBlockStore->overwrite(key, std::move(encryptedWithFormatHeader));
+  return cpputils::make_unique_ref<EncryptedBlock>(std::move(baseBlock), encKey, std::move(plaintextWithHeader));
+}
+
 template<class Cipher>
 cpputils::Data EncryptedBlock<Cipher>::_prependFormatHeader(const cpputils::Data &data) {
   cpputils::Data dataWithHeader(sizeof(FORMAT_VERSION_HEADER) + data.size());
diff --git a/src/blockstore/implementations/encrypted/EncryptedBlockStore.h b/src/blockstore/implementations/encrypted/EncryptedBlockStore.h
index e921088f..62bd52b5 100644
--- a/src/blockstore/implementations/encrypted/EncryptedBlockStore.h
+++ b/src/blockstore/implementations/encrypted/EncryptedBlockStore.h
@@ -20,6 +20,7 @@ public:
   Key createKey() override;
   boost::optional<cpputils::unique_ref<Block>> tryCreate(const Key &key, cpputils::Data data) override;
   boost::optional<cpputils::unique_ref<Block>> load(const Key &key) override;
+  cpputils::unique_ref<Block> overwrite(const blockstore::Key &key, cpputils::Data data) override;
   void remove(const Key &key) override;
   uint64_t numBlocks() const override;
   uint64_t estimateNumFreeBytes() const override;
@@ -37,7 +38,6 @@ private:
 };
 
 
-
 template<class Cipher>
 EncryptedBlockStore<Cipher>::EncryptedBlockStore(cpputils::unique_ref<BlockStore> baseBlockStore, const typename Cipher::EncryptionKey &encKey)
  : _baseBlockStore(std::move(baseBlockStore)), _encKey(encKey) {
@@ -69,6 +69,11 @@ boost::optional<cpputils::unique_ref<Block>> EncryptedBlockStore<Cipher>::load(c
   return boost::optional<cpputils::unique_ref<Block>>(EncryptedBlock<Cipher>::TryDecrypt(std::move(*block), _encKey));
 }
 
+template<class Cipher>
+cpputils::unique_ref<Block> EncryptedBlockStore<Cipher>::overwrite(const blockstore::Key &key, cpputils::Data data) {
+  return EncryptedBlock<Cipher>::Overwrite(_baseBlockStore.get(), key, std::move(data), _encKey);
+}
+
 template<class Cipher>
 void EncryptedBlockStore<Cipher>::remove(const Key &key) {
   return _baseBlockStore->remove(key);
diff --git a/src/blockstore/implementations/inmemory/InMemoryBlock.cpp b/src/blockstore/implementations/inmemory/InMemoryBlock.cpp
index 6ebd50fa..f657c50d 100644
--- a/src/blockstore/implementations/inmemory/InMemoryBlock.cpp
+++ b/src/blockstore/implementations/inmemory/InMemoryBlock.cpp
@@ -26,6 +26,11 @@ InMemoryBlock::InMemoryBlock(const InMemoryBlock &rhs)
 InMemoryBlock::~InMemoryBlock() {
 }
 
+InMemoryBlock &InMemoryBlock::operator=(const InMemoryBlock &rhs) {
+    _data = rhs._data;
+    return *this;
+}
+
 const void *InMemoryBlock::data() const {
   return _data->data();
 }
diff --git a/src/blockstore/implementations/inmemory/InMemoryBlock.h b/src/blockstore/implementations/inmemory/InMemoryBlock.h
index 3f688637..e99a94e8 100644
--- a/src/blockstore/implementations/inmemory/InMemoryBlock.h
+++ b/src/blockstore/implementations/inmemory/InMemoryBlock.h
@@ -14,6 +14,7 @@ public:
   InMemoryBlock(const Key &key, cpputils::Data size);
   InMemoryBlock(const InMemoryBlock &rhs);
   ~InMemoryBlock();
+  InMemoryBlock &operator=(const InMemoryBlock &rhs);
 
   const void *data() const override;
   void write(const void *source, uint64_t offset, uint64_t size) override;
diff --git a/src/blockstore/implementations/inmemory/InMemoryBlockStore.cpp b/src/blockstore/implementations/inmemory/InMemoryBlockStore.cpp
index 20a66b2a..70ab1b80 100644
--- a/src/blockstore/implementations/inmemory/InMemoryBlockStore.cpp
+++ b/src/blockstore/implementations/inmemory/InMemoryBlockStore.cpp
@@ -42,6 +42,19 @@ optional<unique_ref<Block>> InMemoryBlockStore::load(const Key &key) {
   }
 }
 
+unique_ref<Block> InMemoryBlockStore::overwrite(const Key &key, Data data) {
+  InMemoryBlock newBlock(key, std::move(data));
+  auto insert_result = _blocks.emplace(key, newBlock);
+
+  if (!insert_result.second) {
+    // If block already exists, overwrite it.
+    insert_result.first->second = newBlock;
+  }
+
+  //Return a pointer to the stored InMemoryBlock
+  return make_unique_ref<InMemoryBlock>(insert_result.first->second);
+}
+
 void InMemoryBlockStore::remove(const Key &key) {
   int numRemoved = _blocks.erase(key);
   ASSERT(1==numRemoved, "Didn't find block to remove");
diff --git a/src/blockstore/implementations/inmemory/InMemoryBlockStore.h b/src/blockstore/implementations/inmemory/InMemoryBlockStore.h
index aeaf14a1..33c0afba 100644
--- a/src/blockstore/implementations/inmemory/InMemoryBlockStore.h
+++ b/src/blockstore/implementations/inmemory/InMemoryBlockStore.h
@@ -19,6 +19,7 @@ public:
 
   boost::optional<cpputils::unique_ref<Block>> tryCreate(const Key &key, cpputils::Data data) override;
   boost::optional<cpputils::unique_ref<Block>> load(const Key &key) override;
+  cpputils::unique_ref<Block> overwrite(const blockstore::Key &key, cpputils::Data data) override;
   void remove(const Key &key) override;
   uint64_t numBlocks() const override;
   uint64_t estimateNumFreeBytes() const override;
diff --git a/src/blockstore/implementations/mock/MockBlockStore.h b/src/blockstore/implementations/mock/MockBlockStore.h
index d2d5113f..576833d6 100644
--- a/src/blockstore/implementations/mock/MockBlockStore.h
+++ b/src/blockstore/implementations/mock/MockBlockStore.h
@@ -41,6 +41,11 @@ namespace blockstore {
                 return boost::optional<cpputils::unique_ref<Block>>(cpputils::make_unique_ref<MockBlock>(std::move(*base), this));
             }
 
+            cpputils::unique_ref<Block> overwrite(const Key &key, cpputils::Data data) override {
+                _increaseNumWrittenBlocks(key);
+                return _baseBlockStore->overwrite(key, std::move(data));
+            }
+
             void remove(const Key &key) override {
                 _increaseNumRemovedBlocks(key);
                 return _baseBlockStore->remove(key);
diff --git a/src/blockstore/implementations/ondisk/OnDiskBlock.cpp b/src/blockstore/implementations/ondisk/OnDiskBlock.cpp
index f397b727..517590d6 100644
--- a/src/blockstore/implementations/ondisk/OnDiskBlock.cpp
+++ b/src/blockstore/implementations/ondisk/OnDiskBlock.cpp
@@ -86,6 +86,14 @@ optional<unique_ref<OnDiskBlock>> OnDiskBlock::CreateOnDisk(const bf::path &root
   return std::move(block);
 }
 
+unique_ref<OnDiskBlock> OnDiskBlock::OverwriteOnDisk(const bf::path &rootdir, const Key &key, Data data) {
+  auto filepath = _getFilepath(rootdir, key);
+  bf::create_directory(filepath.parent_path());
+  auto block = make_unique_ref<OnDiskBlock>(key, filepath, std::move(data));
+  block->_storeToDisk();
+  return std::move(block);
+}
+
 void OnDiskBlock::RemoveFromDisk(const bf::path &rootdir, const Key &key) {
   auto filepath = _getFilepath(rootdir, key);
   ASSERT(bf::is_regular_file(filepath), "Block not found on disk");
diff --git a/src/blockstore/implementations/ondisk/OnDiskBlock.h b/src/blockstore/implementations/ondisk/OnDiskBlock.h
index 36dd7c37..a3714f08 100644
--- a/src/blockstore/implementations/ondisk/OnDiskBlock.h
+++ b/src/blockstore/implementations/ondisk/OnDiskBlock.h
@@ -26,6 +26,7 @@ public:
 
   static boost::optional<cpputils::unique_ref<OnDiskBlock>> LoadFromDisk(const boost::filesystem::path &rootdir, const Key &key);
   static boost::optional<cpputils::unique_ref<OnDiskBlock>> CreateOnDisk(const boost::filesystem::path &rootdir, const Key &key, cpputils::Data data);
+  static cpputils::unique_ref<OnDiskBlock> OverwriteOnDisk(const boost::filesystem::path &rootdir, const Key &key, cpputils::Data data);
   static void RemoveFromDisk(const boost::filesystem::path &rootdir, const Key &key);
 
   const void *data() const override;
diff --git a/src/blockstore/implementations/ondisk/OnDiskBlockStore.cpp b/src/blockstore/implementations/ondisk/OnDiskBlockStore.cpp
index a055d90c..75ec9c36 100644
--- a/src/blockstore/implementations/ondisk/OnDiskBlockStore.cpp
+++ b/src/blockstore/implementations/ondisk/OnDiskBlockStore.cpp
@@ -65,6 +65,10 @@ optional<unique_ref<Block>> OnDiskBlockStore::tryCreate(const Key &key, Data dat
   return unique_ref<Block>(std::move(*result));
 }
 
+unique_ref<Block> OnDiskBlockStore::overwrite(const Key &key, Data data) {
+  return OnDiskBlock::OverwriteOnDisk(_rootdir, key, std::move(data));
+}
+
 optional<unique_ref<Block>> OnDiskBlockStore::load(const Key &key) {
   return optional<unique_ref<Block>>(OnDiskBlock::LoadFromDisk(_rootdir, key));
 }
diff --git a/src/blockstore/implementations/ondisk/OnDiskBlockStore.h b/src/blockstore/implementations/ondisk/OnDiskBlockStore.h
index 26ecdb01..9f419bbd 100644
--- a/src/blockstore/implementations/ondisk/OnDiskBlockStore.h
+++ b/src/blockstore/implementations/ondisk/OnDiskBlockStore.h
@@ -22,6 +22,7 @@ public:
   uint64_t estimateNumFreeBytes() const override;
   uint64_t blockSizeFromPhysicalBlockSize(uint64_t blockSize) const override;
   void forEachBlock(std::function<void (const Key &)> callback) const override;
+  cpputils::unique_ref<Block> overwrite(const blockstore::Key &key, cpputils::Data data) override;
 
 private:
   const boost::filesystem::path _rootdir;
diff --git a/src/blockstore/implementations/parallelaccess/ParallelAccessBlockStore.cpp b/src/blockstore/implementations/parallelaccess/ParallelAccessBlockStore.cpp
index 7cca43e4..39521c91 100644
--- a/src/blockstore/implementations/parallelaccess/ParallelAccessBlockStore.cpp
+++ b/src/blockstore/implementations/parallelaccess/ParallelAccessBlockStore.cpp
@@ -12,6 +12,7 @@ using cpputils::make_unique_ref;
 using boost::none;
 using cpputils::unique_ref;
 using cpputils::make_unique_ref;
+using cpputils::Data;
 using boost::optional;
 using boost::none;
 
@@ -26,7 +27,7 @@ Key ParallelAccessBlockStore::createKey() {
   return _baseBlockStore->createKey();
 }
 
-optional<unique_ref<Block>> ParallelAccessBlockStore::tryCreate(const Key &key, cpputils::Data data) {
+optional<unique_ref<Block>> ParallelAccessBlockStore::tryCreate(const Key &key, Data data) {
   ASSERT(!_parallelAccessStore.isOpened(key), ("Key "+key.ToString()+"already exists").c_str());
   auto block = _baseBlockStore->tryCreate(key, std::move(data));
   if (block == none) {
@@ -44,6 +45,18 @@ optional<unique_ref<Block>> ParallelAccessBlockStore::load(const Key &key) {
   return unique_ref<Block>(std::move(*block));
 }
 
+unique_ref<Block> ParallelAccessBlockStore::overwrite(const Key &key, Data data) {
+  auto onExists = [&data] (BlockRef *block) {
+      if (block->size() != data.size()) {
+        block->resize(data.size());
+      }
+      block->write(data.data(), 0, data.size());
+  };
+  auto onAdd = [this, key, &data] {
+      return _baseBlockStore->overwrite(key, data.copy()); // TODO Without copy?
+  };
+  return _parallelAccessStore.loadOrAdd(key, onExists, onAdd);
+}
 
 void ParallelAccessBlockStore::remove(unique_ref<Block> block) {
   Key key = block->key();
diff --git a/src/blockstore/implementations/parallelaccess/ParallelAccessBlockStore.h b/src/blockstore/implementations/parallelaccess/ParallelAccessBlockStore.h
index 6fd694b9..09bc774e 100644
--- a/src/blockstore/implementations/parallelaccess/ParallelAccessBlockStore.h
+++ b/src/blockstore/implementations/parallelaccess/ParallelAccessBlockStore.h
@@ -18,6 +18,7 @@ public:
   Key createKey() override;
   boost::optional<cpputils::unique_ref<Block>> tryCreate(const Key &key, cpputils::Data data) override;
   boost::optional<cpputils::unique_ref<Block>> load(const Key &key) override;
+  cpputils::unique_ref<Block> overwrite(const Key &key, cpputils::Data data) override;
   void remove(const Key &key) override;
   void remove(cpputils::unique_ref<Block> node) override;
   uint64_t numBlocks() const override;
diff --git a/src/blockstore/implementations/testfake/FakeBlockStore.cpp b/src/blockstore/implementations/testfake/FakeBlockStore.cpp
index 7453a07d..8bc08160 100644
--- a/src/blockstore/implementations/testfake/FakeBlockStore.cpp
+++ b/src/blockstore/implementations/testfake/FakeBlockStore.cpp
@@ -31,6 +31,21 @@ optional<unique_ref<Block>> FakeBlockStore::tryCreate(const Key &key, Data data)
   return _load(key);
 }
 
+unique_ref<Block> FakeBlockStore::overwrite(const Key &key, Data data) {
+  std::unique_lock<std::mutex> lock(_mutex);
+  auto insert_result = _blocks.emplace(key, data.copy());
+
+  if (!insert_result.second) {
+    // If block already exists, overwrite it.
+    insert_result.first->second = std::move(data);
+  }
+
+  //Return a pointer to the stored FakeBlock
+  auto loaded = _load(key);
+  ASSERT(loaded != none, "Block was just created or written. Should exist.");
+  return std::move(*loaded);
+}
+
 optional<unique_ref<Block>> FakeBlockStore::load(const Key &key) {
   std::unique_lock<std::mutex> lock(_mutex);
   return _load(key);
diff --git a/src/blockstore/implementations/testfake/FakeBlockStore.h b/src/blockstore/implementations/testfake/FakeBlockStore.h
index 365914f1..3d17af38 100644
--- a/src/blockstore/implementations/testfake/FakeBlockStore.h
+++ b/src/blockstore/implementations/testfake/FakeBlockStore.h
@@ -32,6 +32,7 @@ public:
   FakeBlockStore();
 
   boost::optional<cpputils::unique_ref<Block>> tryCreate(const Key &key, cpputils::Data data) override;
+  cpputils::unique_ref<Block> overwrite(const blockstore::Key &key, cpputils::Data data) override;
   boost::optional<cpputils::unique_ref<Block>> load(const Key &key) override;
   void remove(const Key &key) override;
   uint64_t numBlocks() const override;
diff --git a/src/blockstore/implementations/versioncounting/KnownBlockVersions.cpp b/src/blockstore/implementations/versioncounting/KnownBlockVersions.cpp
index 1c890af2..2207ff79 100644
--- a/src/blockstore/implementations/versioncounting/KnownBlockVersions.cpp
+++ b/src/blockstore/implementations/versioncounting/KnownBlockVersions.cpp
@@ -72,10 +72,10 @@ bool KnownBlockVersions::checkAndUpdateVersion(uint32_t clientId, const Key &key
     return true;
 }
 
-uint64_t KnownBlockVersions::incrementVersion(const Key &key, uint64_t lastVersion) {
+uint64_t KnownBlockVersions::incrementVersion(const Key &key) {
     unique_lock<mutex> lock(_mutex);
     uint64_t &found = _knownVersions[{_myClientId, key}]; // If the entry doesn't exist, this creates it with value 0.
-    uint64_t newVersion = std::max(lastVersion + 1, found + 1);
+    uint64_t newVersion = found + 1;
     if (newVersion == std::numeric_limits<uint64_t>::max()) {
         // It's *very* unlikely we ever run out of version numbers in 64bit...but just to be sure...
         throw std::runtime_error("Version overflow");
diff --git a/src/blockstore/implementations/versioncounting/KnownBlockVersions.h b/src/blockstore/implementations/versioncounting/KnownBlockVersions.h
index 4142f81e..12a51e5c 100644
--- a/src/blockstore/implementations/versioncounting/KnownBlockVersions.h
+++ b/src/blockstore/implementations/versioncounting/KnownBlockVersions.h
@@ -24,7 +24,7 @@ namespace blockstore {
             __attribute__((warn_unused_result))
             bool checkAndUpdateVersion(uint32_t clientId, const Key &key, uint64_t version);
 
-            uint64_t incrementVersion(const Key &key, uint64_t lastVersion);
+            uint64_t incrementVersion(const Key &key);
 
             void markBlockAsDeleted(const Key &key);
 
diff --git a/src/blockstore/implementations/versioncounting/VersionCountingBlock.cpp b/src/blockstore/implementations/versioncounting/VersionCountingBlock.cpp
index 1641d5a7..186b1157 100644
--- a/src/blockstore/implementations/versioncounting/VersionCountingBlock.cpp
+++ b/src/blockstore/implementations/versioncounting/VersionCountingBlock.cpp
@@ -10,7 +10,7 @@ namespace blockstore {
 
 #ifndef CRYFS_NO_COMPATIBILITY
         void VersionCountingBlock::migrateFromBlockstoreWithoutVersionNumbers(cpputils::unique_ref<Block> baseBlock, KnownBlockVersions *knownBlockVersions) {
-            uint64_t version = knownBlockVersions->incrementVersion(baseBlock->key(), VERSION_ZERO);
+            uint64_t version = knownBlockVersions->incrementVersion(baseBlock->key());
 
             cpputils::Data data(baseBlock->size());
             std::memcpy(data.data(), baseBlock->data(), data.size());
diff --git a/src/blockstore/implementations/versioncounting/VersionCountingBlock.h b/src/blockstore/implementations/versioncounting/VersionCountingBlock.h
index 3c9f929a..8b91ce44 100644
--- a/src/blockstore/implementations/versioncounting/VersionCountingBlock.h
+++ b/src/blockstore/implementations/versioncounting/VersionCountingBlock.h
@@ -28,6 +28,7 @@ namespace versioncounting {
 class VersionCountingBlock final: public Block {
 public:
   static boost::optional<cpputils::unique_ref<VersionCountingBlock>> TryCreateNew(BlockStore *baseBlockStore, const Key &key, cpputils::Data data, VersionCountingBlockStore *blockStore);
+  static cpputils::unique_ref<VersionCountingBlock> Overwrite(BlockStore *baseBlockStore, const Key &key, cpputils::Data data, VersionCountingBlockStore *blockStore);
   static cpputils::unique_ref<VersionCountingBlock> Load(cpputils::unique_ref<Block> baseBlock, VersionCountingBlockStore *blockStore);
 
   static uint64_t blockSizeFromPhysicalBlockSize(uint64_t blockSize);
@@ -53,7 +54,6 @@ private:
   VersionCountingBlockStore *_blockStore;
   cpputils::unique_ref<Block> _baseBlock;
   cpputils::Data _dataWithHeader;
-  uint64_t _version;
   bool _dataChanged;
   std::mutex _mutex;
 
@@ -78,7 +78,7 @@ public:
 
 
 inline boost::optional<cpputils::unique_ref<VersionCountingBlock>> VersionCountingBlock::TryCreateNew(BlockStore *baseBlockStore, const Key &key, cpputils::Data data, VersionCountingBlockStore *blockStore) {
-  uint64_t version = blockStore->knownBlockVersions()->incrementVersion(key, VERSION_ZERO);
+  uint64_t version = blockStore->knownBlockVersions()->incrementVersion(key);
 
   cpputils::Data dataWithHeader = _prependHeaderToData(blockStore->knownBlockVersions()->myClientId(), version, std::move(data));
   auto baseBlock = baseBlockStore->tryCreate(key, dataWithHeader.copy()); // TODO Copy necessary?
@@ -90,6 +90,14 @@ inline boost::optional<cpputils::unique_ref<VersionCountingBlock>> VersionCounti
   return cpputils::make_unique_ref<VersionCountingBlock>(std::move(*baseBlock), std::move(dataWithHeader), blockStore);
 }
 
+inline cpputils::unique_ref<VersionCountingBlock> VersionCountingBlock::Overwrite(BlockStore *baseBlockStore, const Key &key, cpputils::Data data, VersionCountingBlockStore *blockStore) {
+  uint64_t version = blockStore->knownBlockVersions()->incrementVersion(key);
+
+  cpputils::Data dataWithHeader = _prependHeaderToData(blockStore->knownBlockVersions()->myClientId(), version, std::move(data));
+  auto baseBlock = baseBlockStore->overwrite(key, dataWithHeader.copy()); // TODO Copy necessary?
+  return cpputils::make_unique_ref<VersionCountingBlock>(std::move(baseBlock), std::move(dataWithHeader), blockStore);
+}
+
 inline cpputils::Data VersionCountingBlock::_prependHeaderToData(uint32_t myClientId, uint64_t version, cpputils::Data data) {
   static_assert(HEADER_LENGTH == sizeof(FORMAT_VERSION_HEADER) + sizeof(myClientId) + sizeof(version), "Wrong header length");
   cpputils::Data result(data.size() + HEADER_LENGTH);
@@ -140,10 +148,9 @@ inline VersionCountingBlock::VersionCountingBlock(cpputils::unique_ref<Block> ba
    _blockStore(blockStore),
    _baseBlock(std::move(baseBlock)),
    _dataWithHeader(std::move(dataWithHeader)),
-   _version(_readVersion()),
    _dataChanged(false),
    _mutex() {
-  if (_version == std::numeric_limits<uint64_t>::max()) {
+  if (_readVersion() == std::numeric_limits<uint64_t>::max()) {
     throw std::runtime_error("Version overflow when loading. This shouldn't happen because in case of a version number overflow, the block isn't stored at all.");
   }
 }
@@ -180,10 +187,10 @@ inline void VersionCountingBlock::resize(size_t newSize) {
 
 inline void VersionCountingBlock::_storeToBaseBlock() {
   if (_dataChanged) {
-    _version = _blockStore->knownBlockVersions()->incrementVersion(key(), _version);
+    uint64_t version = _blockStore->knownBlockVersions()->incrementVersion(key());
     uint32_t myClientId = _blockStore->knownBlockVersions()->myClientId();
     std::memcpy(_dataWithHeader.dataOffset(CLIENTID_HEADER_OFFSET), &myClientId, sizeof(myClientId));
-    std::memcpy(_dataWithHeader.dataOffset(VERSION_HEADER_OFFSET), &_version, sizeof(_version));
+    std::memcpy(_dataWithHeader.dataOffset(VERSION_HEADER_OFFSET), &version, sizeof(version));
     if (_baseBlock->size() != _dataWithHeader.size()) {
       _baseBlock->resize(_dataWithHeader.size());
     }
diff --git a/src/blockstore/implementations/versioncounting/VersionCountingBlockStore.cpp b/src/blockstore/implementations/versioncounting/VersionCountingBlockStore.cpp
index 6f3738ad..476d02d6 100644
--- a/src/blockstore/implementations/versioncounting/VersionCountingBlockStore.cpp
+++ b/src/blockstore/implementations/versioncounting/VersionCountingBlockStore.cpp
@@ -21,7 +21,7 @@ namespace blockstore {
             return _baseBlockStore->createKey();
         }
 
-        optional<unique_ref<Block>> VersionCountingBlockStore::tryCreate(const Key &key, cpputils::Data data) {
+        optional<unique_ref<Block>> VersionCountingBlockStore::tryCreate(const Key &key, Data data) {
             _checkNoPastIntegrityViolations();
             //TODO Easier implementation? This is only so complicated because of the cast VersionCountingBlock -> Block
             auto result = VersionCountingBlock::TryCreateNew(_baseBlockStore.get(), key, std::move(data), this);
@@ -31,6 +31,11 @@ namespace blockstore {
             return unique_ref<Block>(std::move(*result));
         }
 
+        unique_ref<Block> VersionCountingBlockStore::overwrite(const Key &key, Data data) {
+            _checkNoPastIntegrityViolations();
+            return VersionCountingBlock::Overwrite(_baseBlockStore.get(), key, std::move(data), this);
+        }
+
         optional<unique_ref<Block>> VersionCountingBlockStore::load(const Key &key) {
             _checkNoPastIntegrityViolations();
             auto block = _baseBlockStore->load(key);
diff --git a/src/blockstore/implementations/versioncounting/VersionCountingBlockStore.h b/src/blockstore/implementations/versioncounting/VersionCountingBlockStore.h
index 7ee91900..c429eea1 100644
--- a/src/blockstore/implementations/versioncounting/VersionCountingBlockStore.h
+++ b/src/blockstore/implementations/versioncounting/VersionCountingBlockStore.h
@@ -17,6 +17,7 @@ public:
 
   Key createKey() override;
   boost::optional<cpputils::unique_ref<Block>> tryCreate(const Key &key, cpputils::Data data) override;
+  cpputils::unique_ref<Block> overwrite(const blockstore::Key &key, cpputils::Data data) override;
   boost::optional<cpputils::unique_ref<Block>> load(const Key &key) override;
   void remove(const Key &key) override;
   uint64_t numBlocks() const override;
diff --git a/src/blockstore/interface/BlockStore.h b/src/blockstore/interface/BlockStore.h
index c7704b9f..f7af2fba 100644
--- a/src/blockstore/interface/BlockStore.h
+++ b/src/blockstore/interface/BlockStore.h
@@ -20,6 +20,7 @@ public:
   //TODO Use boost::optional (if key doesn't exist)
   // Return nullptr if block with this key doesn't exists
   virtual boost::optional<cpputils::unique_ref<Block>> load(const Key &key) = 0;
+  virtual cpputils::unique_ref<Block> overwrite(const blockstore::Key &key, cpputils::Data data) = 0;
   virtual void remove(const Key &key) = 0;
   virtual uint64_t numBlocks() const = 0;
   //TODO Test estimateNumFreeBytes in all block stores
diff --git a/src/parallelaccessstore/ParallelAccessStore.h b/src/parallelaccessstore/ParallelAccessStore.h
index 6ff41fe8..2c811549 100644
--- a/src/parallelaccessstore/ParallelAccessStore.h
+++ b/src/parallelaccessstore/ParallelAccessStore.h
@@ -53,6 +53,9 @@ public:
   cpputils::unique_ref<ActualResourceRef> add(const Key &key, cpputils::unique_ref<Resource> resource, std::function<cpputils::unique_ref<ActualResourceRef>(Resource*)> createResourceRef);
   boost::optional<cpputils::unique_ref<ResourceRef>> load(const Key &key);
   boost::optional<cpputils::unique_ref<ResourceRef>> load(const Key &key, std::function<cpputils::unique_ref<ResourceRef>(Resource*)> createResourceRef);
+  //loadOrAdd: If the resource is open, run onExists() on it. If not, run onAdd() and add the created resource. Then return the resource as if load() was called on it.
+  cpputils::unique_ref<ResourceRef> loadOrAdd(const Key &key, std::function<void (ResourceRef*)> onExists, std::function<cpputils::unique_ref<Resource> ()> onAdd);
+  cpputils::unique_ref<ResourceRef> loadOrAdd(const Key &key, std::function<void (ResourceRef*)> onExists, std::function<cpputils::unique_ref<Resource> ()> onAdd, std::function<cpputils::unique_ref<ResourceRef>(Resource*)> createResourceRef);
   void remove(const Key &key, cpputils::unique_ref<ResourceRef> block);
   void remove(const Key &key);
 
@@ -144,6 +147,28 @@ cpputils::unique_ref<ActualResourceRef> ParallelAccessStore<Resource, ResourceRe
   return resourceRef;
 }
 
+template<class Resource, class ResourceRef, class Key>
+cpputils::unique_ref<ResourceRef> ParallelAccessStore<Resource, ResourceRef, Key>::loadOrAdd(const Key &key, std::function<void (ResourceRef*)> onExists, std::function<cpputils::unique_ref<Resource> ()> onAdd) {
+    return loadOrAdd(key, onExists, onAdd, [] (Resource *res) {
+        return cpputils::make_unique_ref<ResourceRef>(res);
+    });
+};
+
+template<class Resource, class ResourceRef, class Key>
+cpputils::unique_ref<ResourceRef> ParallelAccessStore<Resource, ResourceRef, Key>::loadOrAdd(const Key &key, std::function<void (ResourceRef*)> onExists, std::function<cpputils::unique_ref<Resource> ()> onAdd, std::function<cpputils::unique_ref<ResourceRef>(Resource*)> createResourceRef) {
+    std::lock_guard<std::mutex> lock(_mutex);
+    auto found = _openResources.find(key);
+    if (found == _openResources.end()) {
+        auto resource = onAdd();
+        return _add(key, std::move(resource), createResourceRef);
+    } else {
+        auto resourceRef = createResourceRef(found->second.getReference());
+        resourceRef->init(this, key);
+        onExists(resourceRef.get());
+        return std::move(resourceRef);
+    }
+};
+
 template<class Resource, class ResourceRef, class Key>
 boost::optional<cpputils::unique_ref<ResourceRef>> ParallelAccessStore<Resource, ResourceRef, Key>::load(const Key &key) {
   return load(key, [] (Resource *res) {
diff --git a/test/blockstore/implementations/versioncounting/KnownBlockVersionsTest.cpp b/test/blockstore/implementations/versioncounting/KnownBlockVersionsTest.cpp
index 11575cae..f35cc180 100644
--- a/test/blockstore/implementations/versioncounting/KnownBlockVersionsTest.cpp
+++ b/test/blockstore/implementations/versioncounting/KnownBlockVersionsTest.cpp
@@ -70,46 +70,19 @@ TEST_F(KnownBlockVersionsTest, myClientId_isConsistent) {
     EXPECT_EQ(testobj.myClientId(), testobj.myClientId());
 }
 
-TEST_F(KnownBlockVersionsTest, incrementVersion_newentry_versionzero) {
-    auto version = testobj.incrementVersion(key, VersionCountingBlock::VERSION_ZERO);
+TEST_F(KnownBlockVersionsTest, incrementVersion_newentry) {
+    auto version = testobj.incrementVersion(key);
     EXPECT_EQ(1u, version);
     EXPECT_EQ(1u, testobj.getBlockVersion(testobj.myClientId(), key));
 }
 
-TEST_F(KnownBlockVersionsTest, incrementVersion_newentry_versionnotzero) {
-    auto version = testobj.incrementVersion(key, 5);
+TEST_F(KnownBlockVersionsTest, incrementVersion_oldentry) {
+    setVersion(&testobj, testobj.myClientId(), key, 5);
+    auto version = testobj.incrementVersion(key);
     EXPECT_EQ(6u, version);
     EXPECT_EQ(6u, testobj.getBlockVersion(testobj.myClientId(), key));
 }
 
-TEST_F(KnownBlockVersionsTest, incrementVersion_oldentry_sameVersion) {
-    setVersion(&testobj, testobj.myClientId(), key, 5);
-    auto version = testobj.incrementVersion(key, 5);
-    EXPECT_EQ(6u, version);
-    EXPECT_EQ(6u, testobj.getBlockVersion(testobj.myClientId(), key));
-}
-
-TEST_F(KnownBlockVersionsTest, incrementVersion_oldentry_lowerVersion1) {
-    setVersion(&testobj, testobj.myClientId(), key, 5);
-    auto version = testobj.incrementVersion(key, 4);
-    EXPECT_EQ(6u, version);
-    EXPECT_EQ(6u, testobj.getBlockVersion(testobj.myClientId(), key));
-}
-
-TEST_F(KnownBlockVersionsTest, incrementVersion_oldentry_lowerVersion2) {
-    setVersion(&testobj, testobj.myClientId(), key, 5);
-    auto version = testobj.incrementVersion(key, 3);
-    EXPECT_EQ(6u, version);
-    EXPECT_EQ(6u, testobj.getBlockVersion(testobj.myClientId(), key));
-}
-
-TEST_F(KnownBlockVersionsTest, incrementVersion_oldentry_higherVersion) {
-    setVersion(&testobj, testobj.myClientId(), key, 5);
-    auto version = testobj.incrementVersion(key, 6);
-    EXPECT_EQ(7u, version);
-    EXPECT_EQ(7u, testobj.getBlockVersion(testobj.myClientId(), key));
-}
-
 TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_newentry) {
     EXPECT_TRUE(testobj.checkAndUpdateVersion(clientId, key, 5));
     EXPECT_EQ(5u, testobj.getBlockVersion(clientId, key));
@@ -179,7 +152,7 @@ TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientHigherVer
 }
 
 TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientLowerVersion_oldClientIsSelf) {
-    testobj.incrementVersion(key, 4);
+    setVersion(&testobj, testobj.myClientId(), key, 5);
     EXPECT_TRUE(testobj.checkAndUpdateVersion(clientId2, key, 7));
     EXPECT_FALSE(testobj.checkAndUpdateVersion(testobj.myClientId(), key, 3));
     EXPECT_EQ(5u, testobj.getBlockVersion(testobj.myClientId(), key));
@@ -187,7 +160,7 @@ TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientLowerVers
 }
 
 TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientSameVersion_oldClientIsSelf) {
-    testobj.incrementVersion(key, 4);
+    setVersion(&testobj, testobj.myClientId(), key, 5);
     EXPECT_TRUE(testobj.checkAndUpdateVersion(clientId2, key, 7));
     EXPECT_FALSE(testobj.checkAndUpdateVersion(testobj.myClientId(), key, 5)); // Don't allow rollback to old client's newest block, if it was superseded by another client
     EXPECT_EQ(5u, testobj.getBlockVersion(testobj.myClientId(), key));
@@ -195,7 +168,7 @@ TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientSameVersi
 }
 
 TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientHigherVersion_oldClientIsSelf) {
-    testobj.incrementVersion(key, 4);
+    setVersion(&testobj, testobj.myClientId(), key, 4);
     EXPECT_TRUE(testobj.checkAndUpdateVersion(clientId2, key, 7));
     EXPECT_TRUE(testobj.checkAndUpdateVersion(testobj.myClientId(), key, 6));
     EXPECT_EQ(6u, testobj.getBlockVersion(testobj.myClientId(), key));
@@ -204,7 +177,7 @@ TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientHigherVer
 
 TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientLowerVersion_newClientIsSelf) {
     setVersion(&testobj, clientId, key, 5);
-    testobj.incrementVersion(key, 6);
+    setVersion(&testobj, testobj.myClientId(), key, 7);
     EXPECT_FALSE(testobj.checkAndUpdateVersion(clientId, key, 3));
     EXPECT_EQ(5u, testobj.getBlockVersion(clientId, key));
     EXPECT_EQ(7u, testobj.getBlockVersion(testobj.myClientId(), key));
@@ -212,7 +185,7 @@ TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientLowerVers
 
 TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientSameVersion_newClientIsSelf) {
     setVersion(&testobj, clientId, key, 5);
-    testobj.incrementVersion(key, 6);
+    setVersion(&testobj, testobj.myClientId(), key, 7);
     EXPECT_FALSE(testobj.checkAndUpdateVersion(clientId, key, 5)); // Don't allow rollback to old client's newest block, if it was superseded by another client
     EXPECT_EQ(5u, testobj.getBlockVersion(clientId, key));
     EXPECT_EQ(7u, testobj.getBlockVersion(testobj.myClientId(), key));
@@ -220,7 +193,7 @@ TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientSameVersi
 
 TEST_F(KnownBlockVersionsTest, checkAndUpdateVersion_oldentry_oldClientHigherVersion_newClientIsSelf) {
     setVersion(&testobj, clientId, key, 5);
-    testobj.incrementVersion(key, 6);
+    setVersion(&testobj, testobj.myClientId(), key, 7);
     EXPECT_TRUE(testobj.checkAndUpdateVersion(clientId, key, 6));
     EXPECT_EQ(6u, testobj.getBlockVersion(clientId, key));
     EXPECT_EQ(7u, testobj.getBlockVersion(testobj.myClientId(), key));
diff --git a/test/blockstore/interface/helpers/BlockStoreWithRandomKeysTest.cpp b/test/blockstore/interface/helpers/BlockStoreWithRandomKeysTest.cpp
index d4f7a8fd..79861108 100644
--- a/test/blockstore/interface/helpers/BlockStoreWithRandomKeysTest.cpp
+++ b/test/blockstore/interface/helpers/BlockStoreWithRandomKeysTest.cpp
@@ -24,6 +24,10 @@ public:
     return cpputils::nullcheck(std::unique_ptr<Block>(do_create(key, data)));
   }
   MOCK_METHOD2(do_create, Block*(const Key &, const Data &data));
+  unique_ref<Block> overwrite(const Key &key, Data data) {
+    return cpputils::nullcheck(std::unique_ptr<Block>(do_overwrite(key, data))).value();
+  }
+  MOCK_METHOD2(do_overwrite, Block*(const Key &, const Data &data));
   optional<unique_ref<Block>> load(const Key &key) {
     return cpputils::nullcheck(std::unique_ptr<Block>(do_load(key)));
   }
diff --git a/test/blockstore/testutils/BlockStoreTest.h b/test/blockstore/testutils/BlockStoreTest.h
index abc32b01..29e509ec 100644
--- a/test/blockstore/testutils/BlockStoreTest.h
+++ b/test/blockstore/testutils/BlockStoreTest.h
@@ -318,7 +318,15 @@ REGISTER_TYPED_TEST_CASE_P(BlockStoreTest,
     NumBlocksIsCorrectAfterRemovingABlock_DeleteByKey,
     WriteAndReadImmediately,
     WriteAndReadAfterLoading,
-    OverwriteAndRead,
+    WriteTwiceAndRead,
+    OverwriteSameSizeAndReadImmediately,
+    OverwriteSameSizeAndReadAfterLoading,
+    OverwriteSmallerSizeAndReadImmediately,
+    OverwriteSmallerSizeAndReadAfterLoading,
+    OverwriteLargerSizeAndReadAfterLoading,
+    OverwriteLargerSizeAndReadImmediately,
+    OverwriteNonexistingAndReadAfterLoading,
+    OverwriteNonexistingAndReadImmediately,
     CanRemoveModifiedBlock,
     ForEachBlock_zeroblocks,
     ForEachBlock_oneblock,
diff --git a/test/blockstore/testutils/BlockStoreTest_Data.h b/test/blockstore/testutils/BlockStoreTest_Data.h
index be0e4f1f..3804faea 100644
--- a/test/blockstore/testutils/BlockStoreTest_Data.h
+++ b/test/blockstore/testutils/BlockStoreTest_Data.h
@@ -35,7 +35,7 @@ public:
     EXPECT_DATA_IS_ZEROES_OUTSIDE_OF(*loaded_block, testData.offset, testData.count);
   }
 
-  void TestOverwriteAndRead() {
+  void TestWriteTwiceAndRead() {
     auto block = blockStore->create(cpputils::Data(testData.blocksize));
     block->write(backgroundData.data(), 0, testData.blocksize);
     block->write(foregroundData.data(), testData.offset, testData.count);
@@ -43,6 +43,66 @@ public:
     EXPECT_DATA_READS_AS_OUTSIDE_OF(backgroundData, *block, testData.offset, testData.count);
   }
 
+  void TestOverwriteSameSizeAndReadImmediately() {
+    auto key = blockStore->create(cpputils::Data(testData.blocksize))->key();
+    auto block = blockStore->overwrite(key, backgroundData.copy());
+    EXPECT_EQ(testData.blocksize, block->size());
+    EXPECT_DATA_READS_AS(backgroundData, *block, 0, testData.blocksize);
+  }
+
+  void TestOverwriteSameSizeAndReadAfterLoading() {
+    auto key = blockStore->create(cpputils::Data(testData.blocksize))->key();
+    blockStore->overwrite(key, backgroundData.copy());
+    auto block = blockStore->load(key).value();
+    EXPECT_EQ(testData.blocksize, block->size());
+    EXPECT_DATA_READS_AS(backgroundData, *block, 0, testData.blocksize);
+  }
+
+  void TestOverwriteSmallerSizeAndReadImmediately() {
+    auto key = blockStore->create(cpputils::Data(testData.blocksize))->key();
+    auto block = blockStore->overwrite(key, foregroundData.copy());
+    EXPECT_EQ(testData.count, block->size());
+    EXPECT_DATA_READS_AS(foregroundData, *block, 0, testData.count);
+  }
+
+  void TestOverwriteSmallerSizeAndReadAfterLoading() {
+    auto key = blockStore->create(cpputils::Data(testData.blocksize))->key();
+    blockStore->overwrite(key, foregroundData.copy());
+    auto block = blockStore->load(key).value();
+    EXPECT_EQ(testData.count, block->size());
+    EXPECT_DATA_READS_AS(foregroundData, *block, 0, testData.count);
+  }
+
+  void TestOverwriteLargerSizeAndReadImmediately() {
+    auto key = blockStore->create(cpputils::Data(testData.count))->key();
+    auto block = blockStore->overwrite(key, backgroundData.copy());
+    EXPECT_EQ(testData.blocksize, block->size());
+    EXPECT_DATA_READS_AS(backgroundData, *block, 0, testData.blocksize);
+  }
+
+  void TestOverwriteLargerSizeAndReadAfterLoading() {
+    auto key = blockStore->create(cpputils::Data(testData.count))->key();
+    blockStore->overwrite(key, backgroundData.copy());
+    auto block = blockStore->load(key).value();
+    EXPECT_EQ(testData.blocksize, block->size());
+    EXPECT_DATA_READS_AS(backgroundData, *block, 0, testData.blocksize);
+  }
+
+  void TestOverwriteNonexistingAndReadImmediately() {
+    auto key = blockStore->createKey();
+    auto block = blockStore->overwrite(key, backgroundData.copy());
+    EXPECT_EQ(testData.blocksize, block->size());
+    EXPECT_DATA_READS_AS(backgroundData, *block, 0, testData.blocksize);
+  }
+
+  void TestOverwriteNonexistingAndReadAfterLoading() {
+    auto key = blockStore->createKey();
+    blockStore->overwrite(key, backgroundData.copy());
+    auto block = blockStore->load(key).value();
+    EXPECT_EQ(testData.blocksize, block->size());
+    EXPECT_DATA_READS_AS(backgroundData, *block, 0, testData.blocksize);
+  }
+
 private:
   cpputils::unique_ref<blockstore::BlockStore> blockStore;
   DataRange testData;
@@ -102,6 +162,14 @@ inline std::vector<DataRange> DATA_RANGES() {
 
 TYPED_TEST_P_FOR_ALL_DATA_RANGES(WriteAndReadImmediately);
 TYPED_TEST_P_FOR_ALL_DATA_RANGES(WriteAndReadAfterLoading);
-TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteAndRead);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(WriteTwiceAndRead);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteSameSizeAndReadImmediately);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteSameSizeAndReadAfterLoading);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteSmallerSizeAndReadImmediately);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteSmallerSizeAndReadAfterLoading);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteLargerSizeAndReadImmediately);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteLargerSizeAndReadAfterLoading);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteNonexistingAndReadImmediately);
+TYPED_TEST_P_FOR_ALL_DATA_RANGES(OverwriteNonexistingAndReadAfterLoading);
 
 #endif