diff --git a/implementations/inmemory/InMemoryBlock.cpp b/implementations/inmemory/InMemoryBlock.cpp
index 387f50ce..78e4b22d 100644
--- a/implementations/inmemory/InMemoryBlock.cpp
+++ b/implementations/inmemory/InMemoryBlock.cpp
@@ -25,12 +25,13 @@ InMemoryBlock::InMemoryBlock(const InMemoryBlock &rhs)
 InMemoryBlock::~InMemoryBlock() {
 }
 
-void *InMemoryBlock::data() {
+const void *InMemoryBlock::data() const {
   return _data->data();
 }
 
-const void *InMemoryBlock::data() const {
-  return _data->data();
+void InMemoryBlock::write(const void *source, uint64_t offset, uint64_t size) {
+  assert(offset <= _data->size() && offset + size <= _data->size()); //Also check offset < _data->size() because of possible overflow in the addition
+  std::memcpy((uint8_t*)_data->data()+offset, source, size);
 }
 
 size_t InMemoryBlock::size() const {
diff --git a/implementations/inmemory/InMemoryBlock.h b/implementations/inmemory/InMemoryBlock.h
index 833eec74..bc805401 100644
--- a/implementations/inmemory/InMemoryBlock.h
+++ b/implementations/inmemory/InMemoryBlock.h
@@ -15,8 +15,8 @@ public:
   InMemoryBlock(const InMemoryBlock &rhs);
   virtual ~InMemoryBlock();
 
-  void *data() override;
   const void *data() const override;
+  void write(const void *source, uint64_t offset, uint64_t size) override;
 
   void flush() override;
 
diff --git a/implementations/ondisk/OnDiskBlock.cpp b/implementations/ondisk/OnDiskBlock.cpp
index ee4aa70f..44911d3e 100644
--- a/implementations/ondisk/OnDiskBlock.cpp
+++ b/implementations/ondisk/OnDiskBlock.cpp
@@ -31,12 +31,13 @@ OnDiskBlock::~OnDiskBlock() {
   _storeToDisk();
 }
 
-void *OnDiskBlock::data() {
+const void *OnDiskBlock::data() const {
   return _data.data();
 }
 
-const void *OnDiskBlock::data() const {
-  return _data.data();
+void OnDiskBlock::write(const void *source, uint64_t offset, uint64_t size) {
+  assert(offset <= _data.size() && offset + size <= _data.size()); //Also check offset < _data->size() because of possible overflow in the addition
+  std::memcpy((uint8_t*)_data.data()+offset, source, size);
 }
 
 size_t OnDiskBlock::size() const {
diff --git a/implementations/ondisk/OnDiskBlock.h b/implementations/ondisk/OnDiskBlock.h
index f4271cd4..db0bf19d 100644
--- a/implementations/ondisk/OnDiskBlock.h
+++ b/implementations/ondisk/OnDiskBlock.h
@@ -21,8 +21,8 @@ public:
   static std::unique_ptr<OnDiskBlock> CreateOnDisk(const boost::filesystem::path &rootdir, const Key &key, size_t size);
   static void RemoveFromDisk(const boost::filesystem::path &rootdir, const Key &key);
 
-  void *data() override;
   const void *data() const override;
+  void write(const void *source, uint64_t offset, uint64_t size) override;
 
   void flush() override;
 
diff --git a/implementations/testfake/FakeBlock.cpp b/implementations/testfake/FakeBlock.cpp
index 4dc2949e..65f48964 100644
--- a/implementations/testfake/FakeBlock.cpp
+++ b/implementations/testfake/FakeBlock.cpp
@@ -22,12 +22,13 @@ FakeBlock::~FakeBlock() {
   flush();
 }
 
-void *FakeBlock::data() {
+const void *FakeBlock::data() const {
   return _data->data();
 }
 
-const void *FakeBlock::data() const {
-  return _data->data();
+void FakeBlock::write(const void *source, uint64_t offset, uint64_t size) {
+  assert(offset <= _data->size() && offset + size <= _data->size()); //Also check offset < _data->size() because of possible overflow in the addition
+  std::memcpy((uint8_t*)_data->data()+offset, source, size);
 }
 
 size_t FakeBlock::size() const {
diff --git a/implementations/testfake/FakeBlock.h b/implementations/testfake/FakeBlock.h
index 97ac5c18..8a1ca87d 100644
--- a/implementations/testfake/FakeBlock.h
+++ b/implementations/testfake/FakeBlock.h
@@ -16,8 +16,8 @@ public:
   FakeBlock(FakeBlockStore *store, const Key &key, std::shared_ptr<Data> data);
   virtual ~FakeBlock();
 
-  void *data() override;
   const void *data() const override;
+  void write(const void *source, uint64_t offset, uint64_t size) override;
 
   void flush() override;
 
diff --git a/interface/Block.h b/interface/Block.h
index 18794a35..8ffe1224 100644
--- a/interface/Block.h
+++ b/interface/Block.h
@@ -11,8 +11,8 @@ class Block {
 public:
   virtual ~Block() {}
 
-  virtual void *data() = 0;
   virtual const void *data() const = 0;
+  virtual void write(const void *source, uint64_t offset, uint64_t size) = 0;
 
   virtual void flush() = 0;
 
diff --git a/test/implementations/ondisk/OnDiskBlockTest/OnDiskBlockFlushTest.cpp b/test/implementations/ondisk/OnDiskBlockTest/OnDiskBlockFlushTest.cpp
index 93668491..d2641e7d 100644
--- a/test/implementations/ondisk/OnDiskBlockTest/OnDiskBlockFlushTest.cpp
+++ b/test/implementations/ondisk/OnDiskBlockTest/OnDiskBlockFlushTest.cpp
@@ -47,7 +47,7 @@ public:
   }
 
   void WriteDataToBlock(const unique_ptr<OnDiskBlock> &block) {
-    std::memcpy(block->data(), randomData.data(), randomData.size());
+    block->write(randomData.data(), 0, randomData.size());
   }
 
   void EXPECT_BLOCK_DATA_CORRECT(const unique_ptr<OnDiskBlock> &block) {
diff --git a/test/interface/helpers/BlockStoreWithRandomKeysTest.cpp b/test/interface/helpers/BlockStoreWithRandomKeysTest.cpp
index 93912252..f4cffc89 100644
--- a/test/interface/helpers/BlockStoreWithRandomKeysTest.cpp
+++ b/test/interface/helpers/BlockStoreWithRandomKeysTest.cpp
@@ -31,8 +31,8 @@ public:
 class BlockMock: public Block {
 public:
   BlockMock(): Block(Key::CreateRandomKey()) {}
-  MOCK_METHOD0(data, void*());
   MOCK_CONST_METHOD0(data, const void*());
+  MOCK_METHOD3(write, void(const void*, uint64_t, uint64_t));
   MOCK_METHOD0(flush, void());
   MOCK_CONST_METHOD0(size, size_t());
   MOCK_CONST_METHOD0(key, const Key&());
diff --git a/test/testutils/BlockStoreTest.h b/test/testutils/BlockStoreTest.h
index 0c251157..02d563df 100644
--- a/test/testutils/BlockStoreTest.h
+++ b/test/testutils/BlockStoreTest.h
@@ -139,13 +139,13 @@ private:
 
   blockstore::Key StoreDataToBlockAndGetKey(const DataBlockFixture &data) {
     auto block = blockStore->create(data.size());
-    std::memcpy(block->data(), data.data(), data.size());
+    block->write(data.data(), 0, data.size());
     return block->key();
   }
 
   std::unique_ptr<blockstore::Block> StoreDataToBlockAndLoadItDirectlyAfterFlushing(const DataBlockFixture &data) {
     auto block = blockStore->create(data.size());
-    std::memcpy(block->data(), data.data(), data.size());
+    block->write(data.data(), 0, data.size());
     block->flush();
     return blockStore->load(block->key());
   }
@@ -160,7 +160,7 @@ private:
   }
 
   void WriteDataToBlock(blockstore::Block *block, const DataBlockFixture &randomData) {
-    std::memcpy(block->data(), randomData.data(), randomData.size());
+    block->write(randomData.data(), 0, randomData.size());
   }
 
   void EXPECT_BLOCK_DATA_CORRECT(const blockstore::Block &block, const DataBlockFixture &randomData) {
diff --git a/test/utils/BlockStoreUtilsTest.cpp b/test/utils/BlockStoreUtilsTest.cpp
index 1ad0e4c0..d1506b2e 100644
--- a/test/utils/BlockStoreUtilsTest.cpp
+++ b/test/utils/BlockStoreUtilsTest.cpp
@@ -51,7 +51,7 @@ TEST_F(BlockStoreUtilsTest_CopyToNewBlock, CopyZeroBlock) {
 
 TEST_F(BlockStoreUtilsTest_CopyToNewBlock, CopyDataBlock) {
   auto block = blockStore->create(SIZE);
-  std::memcpy(block->data(), dataFixture.data(), SIZE);
+  block->write(dataFixture.data(), 0, SIZE);
   auto block2 = copyToNewBlock(blockStore.get(), *block);
 
   EXPECT_EQ(SIZE, block2->size());
@@ -60,7 +60,7 @@ TEST_F(BlockStoreUtilsTest_CopyToNewBlock, CopyDataBlock) {
 
 TEST_F(BlockStoreUtilsTest_CopyToNewBlock, OriginalBlockUnchanged) {
   auto block = blockStore->create(SIZE);
-  std::memcpy(block->data(), dataFixture.data(), SIZE);
+  block->write(dataFixture.data(), 0, SIZE);
   auto block2 = copyToNewBlock(blockStore.get(), *block);
 
   EXPECT_EQ(SIZE, block->size());
@@ -78,7 +78,7 @@ TEST_F(BlockStoreUtilsTest_CopyToExistingBlock, CopyEmptyBlock) {
 TEST_F(BlockStoreUtilsTest_CopyToExistingBlock, CopyZeroBlock) {
   auto block = blockStore->create(SIZE);
   auto block2 = blockStore->create(SIZE);
-  std::memcpy(block2->data(), dataFixture.data(), SIZE);
+  block2->write(dataFixture.data(), 0, SIZE);
   copyTo(block2.get(), *block);
 
   EXPECT_EQ(0, std::memcmp(ZEROES.data(), block2->data(), SIZE));
@@ -86,7 +86,7 @@ TEST_F(BlockStoreUtilsTest_CopyToExistingBlock, CopyZeroBlock) {
 
 TEST_F(BlockStoreUtilsTest_CopyToExistingBlock, CopyDataBlock) {
   auto block = blockStore->create(SIZE);
-  std::memcpy(block->data(), dataFixture.data(), SIZE);
+  block->write(dataFixture.data(), 0, SIZE);
   auto block2 = blockStore->create(SIZE);
   copyTo(block2.get(), *block);
 
@@ -95,7 +95,7 @@ TEST_F(BlockStoreUtilsTest_CopyToExistingBlock, CopyDataBlock) {
 
 TEST_F(BlockStoreUtilsTest_CopyToExistingBlock, OriginalBlockUnchanged) {
   auto block = blockStore->create(SIZE);
-  std::memcpy(block->data(), dataFixture.data(), SIZE);
+  block->write(dataFixture.data(), 0, SIZE);
   auto block2 = blockStore->create(SIZE);
   copyTo(block2.get(), *block);
 
diff --git a/utils/BlockStoreUtils.cpp b/utils/BlockStoreUtils.cpp
index 5e584213..d104265d 100644
--- a/utils/BlockStoreUtils.cpp
+++ b/utils/BlockStoreUtils.cpp
@@ -1,5 +1,6 @@
-#include <messmer/blockstore/interface/BlockStore.h>
-#include <messmer/blockstore/utils/BlockStoreUtils.h>
+#include "../interface/BlockStore.h"
+#include "BlockStoreUtils.h"
+#include "Data.h"
 #include <memory>
 #include <cassert>
 
@@ -16,7 +17,13 @@ unique_ptr<Block> copyToNewBlock(BlockStore *blockStore, const Block &block) {
 
 void copyTo(Block *target, const Block &source) {
   assert(target->size() == source.size());
-  std::memcpy(target->data(), source.data(), source.size());
+  target->write(source.data(), 0, source.size());
+}
+
+void fillWithZeroes(Block *target) {
+  Data zeroes(target->size());
+  zeroes.FillWithZeroes();
+  target->write(zeroes.data(), 0, target->size());
 }
 
 }
diff --git a/utils/BlockStoreUtils.h b/utils/BlockStoreUtils.h
index 7897bf45..616347af 100644
--- a/utils/BlockStoreUtils.h
+++ b/utils/BlockStoreUtils.h
@@ -11,6 +11,9 @@ namespace utils {
 
 std::unique_ptr<Block> copyToNewBlock(BlockStore *blockStore, const Block &block);
 void copyTo(Block *target, const Block &source);
+void fillWithZeroes(Block *target);
+
+//TODO Test fillWithZeroes
 
 }
 }