diff --git a/implementations/onblocks/BlobOnBlocks.cpp b/implementations/onblocks/BlobOnBlocks.cpp
index ebbae610..cb14a9b4 100644
--- a/implementations/onblocks/BlobOnBlocks.cpp
+++ b/implementations/onblocks/BlobOnBlocks.cpp
@@ -33,13 +33,17 @@ void BlobOnBlocks::resize(uint64_t numBytes) {
 
 void BlobOnBlocks::traverseLeaves(uint64_t beginByte, uint64_t sizeBytes, function<void (uint64_t, DataLeafNode *leaf, uint32_t, uint32_t)> func) const {
   uint64_t endByte = beginByte + sizeBytes;
-  assert(endByte <= size());
   uint32_t firstLeaf = beginByte / _datatree->maxBytesPerLeaf();
   uint32_t endLeaf = utils::ceilDivision(endByte, _datatree->maxBytesPerLeaf());
-  _datatree->traverseLeaves(firstLeaf, endLeaf, [&func, beginByte, endByte](DataLeafNode *leaf, uint32_t leafIndex) {
+  bool traversingOutOfRange = _datatree->numStoredBytes() < endByte; //TODO numBytes() inefficient
+  _datatree->traverseLeaves(firstLeaf, endLeaf, [&func, beginByte, endByte, endLeaf, traversingOutOfRange](DataLeafNode *leaf, uint32_t leafIndex) {
     uint64_t indexOfFirstLeafByte = leafIndex * leaf->maxStoreableBytes();
     uint32_t dataBegin = utils::maxZeroSubtraction(beginByte, indexOfFirstLeafByte);
     uint32_t dataEnd = std::min((uint64_t)leaf->maxStoreableBytes(), endByte - indexOfFirstLeafByte);
+    if (leafIndex == endLeaf-1 && traversingOutOfRange) {
+      // If we are traversing an area that didn't exist before, then the last leaf was just created with a wrong size. We have to fix it.
+      leaf->resize(dataEnd);
+    }
     func(indexOfFirstLeafByte, leaf, dataBegin, dataEnd-dataBegin);
   });
 }
@@ -61,7 +65,7 @@ uint64_t BlobOnBlocks::tryRead(void *target, uint64_t offset, uint64_t count) co
 }
 
 void BlobOnBlocks::write(const void *source, uint64_t offset, uint64_t size) {
-  resizeIfSmallerThan(offset + size);
+  //resizeIfSmallerThan(offset + size);
   traverseLeaves(offset, size, [source, offset] (uint64_t indexOfFirstLeafByte, DataLeafNode *leaf, uint32_t leafDataOffset, uint32_t leafDataSize) {
     //TODO Simplify formula, make it easier to understand
     leaf->write((uint8_t*)source + indexOfFirstLeafByte - offset + leafDataOffset, leafDataOffset, leafDataSize);
diff --git a/implementations/onblocks/cachingdatatreestore/CachedDataTreeRef.h b/implementations/onblocks/cachingdatatreestore/CachedDataTreeRef.h
index f026cd84..69a5b6a6 100644
--- a/implementations/onblocks/cachingdatatreestore/CachedDataTreeRef.h
+++ b/implementations/onblocks/cachingdatatreestore/CachedDataTreeRef.h
@@ -21,14 +21,14 @@ public:
     return _baseTree->maxBytesPerLeaf();
   }
 
-  void traverseLeaves(uint32_t beginIndex, uint32_t endIndex, std::function<void (const datanodestore::DataLeafNode*, uint32_t)> func) const {
-    return const_cast<const datatreestore::DataTree*>(_baseTree)->traverseLeaves(beginIndex, endIndex, func);
-  }
-
   void traverseLeaves(uint32_t beginIndex, uint32_t endIndex, std::function<void (datanodestore::DataLeafNode*, uint32_t)> func) {
     return _baseTree->traverseLeaves(beginIndex, endIndex, func);
   }
 
+  uint32_t numLeaves() const {
+    return _baseTree->numLeaves();
+  }
+
   void resizeNumBytes(uint64_t newNumBytes) {
     return _baseTree->resizeNumBytes(newNumBytes);
   }
diff --git a/implementations/onblocks/datatreestore/DataTree.cpp b/implementations/onblocks/datatreestore/DataTree.cpp
index caa53131..ecf3667f 100644
--- a/implementations/onblocks/datatreestore/DataTree.cpp
+++ b/implementations/onblocks/datatreestore/DataTree.cpp
@@ -24,6 +24,7 @@ using std::function;
 using boost::shared_mutex;
 using boost::shared_lock;
 using boost::unique_lock;
+using std::vector;
 
 using cpputils::dynamic_pointer_move;
 using cpputils::optional_ownership_ptr;
@@ -82,8 +83,9 @@ unique_ptr<DataLeafNode> DataTree::addDataLeafAt(DataInnerNode *insertPos) {
   return new_leaf;
 }
 
-optional_ownership_ptr<DataNode> DataTree::createChainOfInnerNodes(unsigned int num, DataLeafNode *leaf) {
-  optional_ownership_ptr<DataNode> chain = cpputils::WithoutOwnership<DataNode>(leaf);
+optional_ownership_ptr<DataNode> DataTree::createChainOfInnerNodes(unsigned int num, DataNode *child) {
+  //TODO This function is implemented twice, once with optional_ownership_ptr, once with unique_ptr. Redundancy!
+  optional_ownership_ptr<DataNode> chain = cpputils::WithoutOwnership<DataNode>(child);
   for(unsigned int i=0; i<num; ++i) {
     auto newnode = _nodeStore->createNewInnerNode(*chain);
     chain = cpputils::WithOwnership<DataNode>(std::move(newnode));
@@ -91,11 +93,27 @@ optional_ownership_ptr<DataNode> DataTree::createChainOfInnerNodes(unsigned int
   return chain;
 }
 
-unique_ptr<DataLeafNode> DataTree::addDataLeafToFullTree() {
+unique_ptr<DataNode> DataTree::createChainOfInnerNodes(unsigned int num, unique_ptr<DataNode> child) {
+  unique_ptr<DataNode> chain = std::move(child);
+  for(unsigned int i=0; i<num; ++i) {
+    chain = _nodeStore->createNewInnerNode(*chain);
+  }
+  return chain;
+}
+
+DataInnerNode* DataTree::increaseTreeDepth(unsigned int levels) {
+  assert(levels >= 1);
   auto copyOfOldRoot = _nodeStore->createNewNodeAsCopyFrom(*_rootNode);
-  auto newRootNode = DataNode::convertToNewInnerNode(std::move(_rootNode), *copyOfOldRoot);
-  auto newLeaf = addDataLeafAt(newRootNode.get());
+  auto chain = createChainOfInnerNodes(levels-1, copyOfOldRoot.get());
+  auto newRootNode = DataNode::convertToNewInnerNode(std::move(_rootNode), *chain);
+  DataInnerNode *result = newRootNode.get();
   _rootNode = std::move(newRootNode);
+  return result;
+}
+
+unique_ptr<DataLeafNode> DataTree::addDataLeafToFullTree() {
+  DataInnerNode *rootNode = increaseTreeDepth(1);
+  auto newLeaf = addDataLeafAt(rootNode);
   return newLeaf;
 }
 
@@ -111,22 +129,46 @@ unique_ptr<DataNode> DataTree::releaseRootNode() {
   return std::move(_rootNode);
 }
 
+//TODO Test numLeaves()
+uint32_t DataTree::numLeaves() const {
+  //TODO Direct calculating the number of leaves would be faster
+  uint64_t currentNumBytes = _numStoredBytes();
+  if(currentNumBytes == 0) {
+    //We always have at least one leaf
+    currentNumBytes = 1;
+  }
+  return utils::ceilDivision(currentNumBytes, _nodeStore->layout().maxBytesPerLeaf());
+}
+
 void DataTree::traverseLeaves(uint32_t beginIndex, uint32_t endIndex, function<void (DataLeafNode*, uint32_t)> func) {
-  const_cast<const DataTree*>(this)->traverseLeaves(beginIndex, endIndex, [func](const DataLeafNode* leaf, uint32_t leafIndex) {
-    func(const_cast<DataLeafNode*>(leaf), leafIndex);
-  });
-}
-
-void DataTree::traverseLeaves(uint32_t beginIndex, uint32_t endIndex, function<void (const DataLeafNode*, uint32_t)> func) const {
-  shared_lock<shared_mutex> lock(_mutex);
+  unique_lock<shared_mutex> lock(_mutex); //TODO Only lock when resizing
   assert(beginIndex <= endIndex);
-  //TODO assert(beginIndex <= numLeaves());
-  //TODO assert(endIndex <= numLeaves());
-  traverseLeaves(_rootNode.get(), 0, beginIndex, endIndex, func);
+
+  uint8_t neededTreeDepth = utils::ceilLog(_nodeStore->layout().maxChildrenPerInnerNode(), endIndex);
+  uint32_t numLeaves = this->numLeaves();
+  if (_rootNode->depth() < neededTreeDepth) {
+    //TODO Test cases that actually increase it here by 0 level / 1 level / more than 1 level
+    increaseTreeDepth(neededTreeDepth - _rootNode->depth());
+  }
+  if (numLeaves < endIndex) {
+    //TODO Can this case be efficiently combined with the traversing?
+    LastLeaf(_rootNode.get())->resize(_nodeStore->layout().maxBytesPerLeaf());
+  }
+  uint32_t lastLeafIndex = std::max(numLeaves, endIndex) - 1;
+  if (numLeaves < beginIndex) {
+    //TODO Test cases with numLeaves < / >= beginIndex
+    return _traverseLeaves(_rootNode.get(), 0, numLeaves, endIndex, [beginIndex, numLeaves, lastLeafIndex, &func](DataLeafNode* node, uint32_t index) {
+      if (index >= beginIndex) {
+        func(node, index);
+      }
+    });
+  } else {
+    return _traverseLeaves(_rootNode.get(), 0, beginIndex, endIndex, func);
+  }
 }
 
-void DataTree::traverseLeaves(const DataNode *root, uint32_t leafOffset, uint32_t beginIndex, uint32_t endIndex, function<void (const DataLeafNode*, uint32_t)> func) const {
-  const DataLeafNode *leaf = dynamic_cast<const DataLeafNode*>(root);
+void DataTree::_traverseLeaves(DataNode *root, uint32_t leafOffset, uint32_t beginIndex, uint32_t endIndex, function<void (DataLeafNode*, uint32_t)> func) {
+  DataLeafNode *leaf = dynamic_cast<DataLeafNode*>(root);
   if (leaf != nullptr) {
     assert(beginIndex <= 1 && endIndex <= 1);
     if (beginIndex == 0 && endIndex == 1) {
@@ -135,20 +177,42 @@ void DataTree::traverseLeaves(const DataNode *root, uint32_t leafOffset, uint32_
     return;
   }
 
-  const DataInnerNode *inner = dynamic_cast<const DataInnerNode*>(root);
+  DataInnerNode *inner = dynamic_cast<DataInnerNode*>(root);
   uint32_t leavesPerChild = leavesPerFullChild(*inner);
   uint32_t beginChild = beginIndex/leavesPerChild;
   uint32_t endChild = utils::ceilDivision(endIndex, leavesPerChild);
+  vector<unique_ptr<DataNode>> children = getOrCreateChildren(inner, beginChild, endChild);
 
   for (uint32_t childIndex = beginChild; childIndex < endChild; ++childIndex) {
     uint32_t childOffset = childIndex * leavesPerChild;
     uint32_t localBeginIndex = utils::maxZeroSubtraction(beginIndex, childOffset);
     uint32_t localEndIndex = std::min(leavesPerChild, endIndex - childOffset);
-    auto child = _nodeStore->load(inner->getChild(childIndex)->key());
-    traverseLeaves(child.get(), leafOffset + childOffset, localBeginIndex, localEndIndex, func);
+    auto child = std::move(children[childIndex-beginChild]);
+    _traverseLeaves(child.get(), leafOffset + childOffset, localBeginIndex, localEndIndex, func);
   }
 }
 
+vector<unique_ptr<DataNode>> DataTree::getOrCreateChildren(DataInnerNode *node, uint32_t begin, uint32_t end) {
+  vector<unique_ptr<DataNode>> children;
+  children.reserve(end-begin);
+  for (uint32_t childIndex = begin; childIndex < std::min(node->numChildren(), end); ++childIndex) {
+    children.emplace_back(_nodeStore->load(node->getChild(childIndex)->key()));
+  }
+  for (uint32_t childIndex = node->numChildren(); childIndex < end; ++childIndex) {
+    children.emplace_back(addChildTo(node));
+  }
+  assert(children.size() == end-begin);
+  return children;
+}
+
+unique_ptr<DataNode> DataTree::addChildTo(DataInnerNode *node) {
+  auto new_leaf = _nodeStore->createNewLeafNode();
+  new_leaf->resize(_nodeStore->layout().maxBytesPerLeaf());
+  auto chain = createChainOfInnerNodes(node->depth()-1, std::move(new_leaf));
+  node->addChild(*chain);
+  return std::move(chain);
+}
+
 uint32_t DataTree::leavesPerFullChild(const DataInnerNode &root) const {
   return utils::intPow(_nodeStore->layout().maxChildrenPerInnerNode(), root.depth()-1);
 }
diff --git a/implementations/onblocks/datatreestore/DataTree.h b/implementations/onblocks/datatreestore/DataTree.h
index 0d726e13..7723b0bd 100644
--- a/implementations/onblocks/datatreestore/DataTree.h
+++ b/implementations/onblocks/datatreestore/DataTree.h
@@ -29,10 +29,10 @@ public:
   const blockstore::Key &key() const;
   uint32_t maxBytesPerLeaf() const;
 
-  void traverseLeaves(uint32_t beginIndex, uint32_t endIndex, std::function<void (const datanodestore::DataLeafNode*, uint32_t)> func) const;
   void traverseLeaves(uint32_t beginIndex, uint32_t endIndex, std::function<void (datanodestore::DataLeafNode*, uint32_t)> func);
   void resizeNumBytes(uint64_t newNumBytes);
 
+  uint32_t numLeaves() const;
   uint64_t numStoredBytes() const;
 
   void flush() const;
@@ -49,19 +49,23 @@ private:
   friend class DataTreeStore;
 
   std::unique_ptr<datanodestore::DataLeafNode> addDataLeafAt(datanodestore::DataInnerNode *insertPos);
-  cpputils::optional_ownership_ptr<datanodestore::DataNode> createChainOfInnerNodes(unsigned int num, datanodestore::DataLeafNode *leaf);
+  cpputils::optional_ownership_ptr<datanodestore::DataNode> createChainOfInnerNodes(unsigned int num, datanodestore::DataNode *child);
+  std::unique_ptr<datanodestore::DataNode> createChainOfInnerNodes(unsigned int num, std::unique_ptr<datanodestore::DataNode> child);
   std::unique_ptr<datanodestore::DataLeafNode> addDataLeafToFullTree();
 
   void deleteLastChildSubtree(datanodestore::DataInnerNode *node);
   void ifRootHasOnlyOneChildReplaceRootWithItsChild();
 
   //TODO Use underscore for private methods
-  void traverseLeaves(const datanodestore::DataNode *root, uint32_t leafOffset, uint32_t beginIndex, uint32_t endIndex, std::function<void (const datanodestore::DataLeafNode*, uint32_t)> func) const;
+  void _traverseLeaves(datanodestore::DataNode *root, uint32_t leafOffset, uint32_t beginIndex, uint32_t endIndex, std::function<void (datanodestore::DataLeafNode*, uint32_t)> func);
   uint32_t leavesPerFullChild(const datanodestore::DataInnerNode &root) const;
   uint64_t _numStoredBytes() const;
   uint64_t _numStoredBytes(const datanodestore::DataNode &root) const;
   cpputils::optional_ownership_ptr<datanodestore::DataLeafNode> LastLeaf(datanodestore::DataNode *root);
   std::unique_ptr<datanodestore::DataLeafNode> LastLeaf(std::unique_ptr<datanodestore::DataNode> root);
+  datanodestore::DataInnerNode* increaseTreeDepth(unsigned int levels);
+  std::vector<std::unique_ptr<datanodestore::DataNode>> getOrCreateChildren(datanodestore::DataInnerNode *node, uint32_t begin, uint32_t end);
+  std::unique_ptr<datanodestore::DataNode> addChildTo(datanodestore::DataInnerNode *node);
 
   DISALLOW_COPY_AND_ASSIGN(DataTree);
 };
diff --git a/implementations/onblocks/utils/Math.cpp b/implementations/onblocks/utils/Math.cpp
index 5bec6846..ab096a36 100644
--- a/implementations/onblocks/utils/Math.cpp
+++ b/implementations/onblocks/utils/Math.cpp
@@ -1,5 +1,7 @@
 #include "Math.h"
 
+#include <cmath>
+
 namespace blobstore {
 namespace onblocks {
 namespace utils {
@@ -23,6 +25,10 @@ uint32_t maxZeroSubtraction(uint32_t minuend, uint32_t subtrahend) {
   return minuend-subtrahend;
 }
 
+uint32_t ceilLog(uint32_t base, uint32_t value) {
+  return std::ceil((long double)std::log(value)/(long double)std::log(base));
+}
+
 }
 }
 }
diff --git a/implementations/onblocks/utils/Math.h b/implementations/onblocks/utils/Math.h
index d5ae3318..5de48a1d 100644
--- a/implementations/onblocks/utils/Math.h
+++ b/implementations/onblocks/utils/Math.h
@@ -11,6 +11,7 @@ namespace utils {
 uint32_t intPow(uint32_t base, uint32_t exponent);
 uint32_t ceilDivision(uint32_t dividend, uint32_t divisor);
 uint32_t maxZeroSubtraction(uint32_t minuend, uint32_t subtrahend);
+uint32_t ceilLog(uint32_t base, uint32_t value);
 
 }
 }
diff --git a/test/implementations/onblocks/BlobReadWriteTest.cpp b/test/implementations/onblocks/BlobReadWriteTest.cpp
index 8de5c928..49054000 100644
--- a/test/implementations/onblocks/BlobReadWriteTest.cpp
+++ b/test/implementations/onblocks/BlobReadWriteTest.cpp
@@ -109,6 +109,12 @@ INSTANTIATE_TEST_CASE_P(BlobReadWriteDataTest, BlobReadWriteDataTest, Values(
   DataRange(BlobReadWriteDataTest::LARGE_SIZE,     BlobReadWriteDataTest::LARGE_SIZE*1/3, BlobReadWriteDataTest::LARGE_SIZE*2/3) // access middle to end
 ));
 
+TEST_P(BlobReadWriteDataTest, WritingDoesntChangeSize) {
+  blob->resize(GetParam().blobsize);
+  blob->write(this->foregroundData.data(), GetParam().offset, GetParam().count);
+  EXPECT_EQ(GetParam().blobsize, blob->size());
+}
+
 TEST_P(BlobReadWriteDataTest, WriteAndReadImmediately) {
   blob->resize(GetParam().blobsize);
   blob->write(this->foregroundData.data(), GetParam().offset, GetParam().count);
diff --git a/test/implementations/onblocks/datatreestore/DataTreeTest_ResizeByTraversing.cpp b/test/implementations/onblocks/datatreestore/DataTreeTest_ResizeByTraversing.cpp
new file mode 100644
index 00000000..3a17d8f4
--- /dev/null
+++ b/test/implementations/onblocks/datatreestore/DataTreeTest_ResizeByTraversing.cpp
@@ -0,0 +1,200 @@
+#include "testutils/DataTreeTest.h"
+#include "testutils/TwoLevelDataFixture.h"
+#include "../../../../implementations/onblocks/utils/Math.h"
+#include <messmer/blockstore/utils/Data.h>
+
+#include <tuple>
+
+using ::testing::WithParamInterface;
+using ::testing::Values;
+using ::testing::Combine;
+using std::tuple;
+using std::get;
+using std::function;
+using std::mem_fn;
+using cpputils::dynamic_pointer_move;
+
+using blobstore::onblocks::datanodestore::DataLeafNode;
+using blobstore::onblocks::datanodestore::DataInnerNode;
+using blobstore::onblocks::datanodestore::DataNode;
+using blobstore::onblocks::datanodestore::DataNodeLayout;
+using blobstore::onblocks::datatreestore::DataTree;
+using blobstore::onblocks::utils::ceilDivision;
+using blockstore::Key;
+using blockstore::Data;
+
+using std::unique_ptr;
+
+class DataTreeTest_ResizeByTraversing: public DataTreeTest {
+public:
+  static constexpr DataNodeLayout LAYOUT = DataNodeLayout(BLOCKSIZE_BYTES);
+
+  unique_ptr<DataTree> CreateTree(unique_ptr<DataNode> root) {
+    Key key = root->key();
+    root.reset();
+    return treeStore.load(key);
+  }
+
+  unique_ptr<DataTree> CreateLeafTreeWithSize(uint32_t size) {
+    return CreateTree(CreateLeafWithSize(size));
+  }
+
+  unique_ptr<DataTree> CreateTwoLeafTreeWithSecondLeafSize(uint32_t size) {
+    return CreateTree(CreateTwoLeafWithSecondLeafSize(size));
+  }
+
+  unique_ptr<DataTree> CreateFullTwoLevelTreeWithLastLeafSize(uint32_t size) {
+    return CreateTree(CreateFullTwoLevelWithLastLeafSize(size));
+  }
+
+  unique_ptr<DataTree> CreateThreeLevelTreeWithTwoChildrenAndLastLeafSize(uint32_t size) {
+    return CreateTree(CreateThreeLevelWithTwoChildrenAndLastLeafSize(size));
+  }
+
+  unique_ptr<DataTree> CreateThreeLevelTreeWithThreeChildrenAndLastLeafSize(uint32_t size) {
+    return CreateTree(CreateThreeLevelWithThreeChildrenAndLastLeafSize(size));
+  }
+
+  unique_ptr<DataTree> CreateFullThreeLevelTreeWithLastLeafSize(uint32_t size) {
+    return CreateTree(CreateFullThreeLevelWithLastLeafSize(size));
+  }
+
+  unique_ptr<DataTree> CreateFourLevelMinDataTreeWithLastLeafSize(uint32_t size) {
+    return CreateTree(CreateFourLevelMinDataWithLastLeafSize(size));
+  }
+
+  void EXPECT_IS_LEFTMAXDATA_TREE(const Key &key) {
+    auto root = nodeStore->load(key);
+    DataInnerNode *inner = dynamic_cast<DataInnerNode*>(root.get());
+    if (inner != nullptr) {
+      for (uint32_t i = 0; i < inner->numChildren()-1; ++i) {
+        EXPECT_IS_MAXDATA_TREE(inner->getChild(i)->key());
+      }
+      EXPECT_IS_LEFTMAXDATA_TREE(inner->LastChild()->key());
+    }
+  }
+
+  void EXPECT_IS_MAXDATA_TREE(const Key &key) {
+    auto root = nodeStore->load(key);
+    DataInnerNode *inner = dynamic_cast<DataInnerNode*>(root.get());
+    if (inner != nullptr) {
+      for (uint32_t i = 0; i < inner->numChildren(); ++i) {
+        EXPECT_IS_MAXDATA_TREE(inner->getChild(i)->key());
+      }
+    } else {
+      DataLeafNode *leaf = dynamic_cast<DataLeafNode*>(root.get());
+      EXPECT_EQ(nodeStore->layout().maxBytesPerLeaf(), leaf->numBytes());
+    }
+  }
+};
+constexpr DataNodeLayout DataTreeTest_ResizeByTraversing::LAYOUT;
+
+class DataTreeTest_ResizeByTraversing_P: public DataTreeTest_ResizeByTraversing, public WithParamInterface<tuple<function<unique_ptr<DataTree>(DataTreeTest_ResizeByTraversing*, uint32_t)>, uint32_t, uint32_t>> {
+public:
+  DataTreeTest_ResizeByTraversing_P()
+    : oldLastLeafSize(get<1>(GetParam())),
+      tree(get<0>(GetParam())(this, oldLastLeafSize)),
+      numberOfLeavesToAdd(get<2>(GetParam())),
+      newNumberOfLeaves(tree->numLeaves()+numberOfLeavesToAdd),
+      ZEROES(LAYOUT.maxBytesPerLeaf())
+  {
+    ZEROES.FillWithZeroes();
+  }
+
+  void GrowTree(const Key &key, uint32_t numLeavesToAdd) {
+    auto tree = treeStore.load(key);
+    GrowTree(tree.get(), numLeavesToAdd);
+  }
+
+  void GrowTree(DataTree *tree, uint32_t numLeavesToAdd) {
+    uint32_t oldNumLeaves = tree->numLeaves();
+    uint32_t newNumLeaves = oldNumLeaves + numLeavesToAdd;
+    //TODO Test cases where beginIndex is inside of the existing leaves
+    tree->traverseLeaves(newNumLeaves-1, newNumLeaves, [] (DataLeafNode*,uint32_t){});
+    tree->flush();
+  }
+
+  unique_ptr<DataLeafNode> LastLeaf(const Key &key) {
+    auto root = nodeStore->load(key);
+    auto leaf = dynamic_pointer_move<DataLeafNode>(root);
+    if (leaf.get() != nullptr) {
+      return leaf;
+    }
+    auto inner = dynamic_pointer_move<DataInnerNode>(root);
+    return LastLeaf(inner->LastChild()->key());
+  }
+
+  uint32_t oldLastLeafSize;
+  unique_ptr<DataTree> tree;
+  uint32_t numberOfLeavesToAdd;
+  uint32_t newNumberOfLeaves;
+  Data ZEROES;
+};
+INSTANTIATE_TEST_CASE_P(DataTreeTest_ResizeByTraversing_P, DataTreeTest_ResizeByTraversing_P,
+  Combine(
+    //Tree we're starting with
+    Values<function<unique_ptr<DataTree>(DataTreeTest_ResizeByTraversing*, uint32_t)>>(
+      mem_fn(&DataTreeTest_ResizeByTraversing::CreateLeafTreeWithSize),
+      mem_fn(&DataTreeTest_ResizeByTraversing::CreateTwoLeafTreeWithSecondLeafSize),
+      mem_fn(&DataTreeTest_ResizeByTraversing::CreateFullTwoLevelTreeWithLastLeafSize),
+      mem_fn(&DataTreeTest_ResizeByTraversing::CreateThreeLevelTreeWithTwoChildrenAndLastLeafSize),
+      mem_fn(&DataTreeTest_ResizeByTraversing::CreateThreeLevelTreeWithThreeChildrenAndLastLeafSize),
+      mem_fn(&DataTreeTest_ResizeByTraversing::CreateFullThreeLevelTreeWithLastLeafSize),
+      mem_fn(&DataTreeTest_ResizeByTraversing::CreateFourLevelMinDataTreeWithLastLeafSize)
+    ),
+    //Last leaf size of the start tree
+    Values(
+      0u,
+      1u,
+      10u,
+      DataTreeTest_ResizeByTraversing::LAYOUT.maxBytesPerLeaf()
+    ),
+    //Number of leaves we're adding
+    Values(
+      1u,
+      2u,
+      DataTreeTest_ResizeByTraversing::LAYOUT.maxChildrenPerInnerNode(),  //Full two level tree
+      2* DataTreeTest_ResizeByTraversing::LAYOUT.maxChildrenPerInnerNode(), //Three level tree with two children
+      3* DataTreeTest_ResizeByTraversing::LAYOUT.maxChildrenPerInnerNode(), //Three level tree with three children
+      DataTreeTest_ResizeByTraversing::LAYOUT.maxChildrenPerInnerNode() * DataTreeTest_ResizeByTraversing::LAYOUT.maxChildrenPerInnerNode(), //Full three level tree
+      DataTreeTest_ResizeByTraversing::LAYOUT.maxChildrenPerInnerNode() * DataTreeTest_ResizeByTraversing::LAYOUT.maxChildrenPerInnerNode() + 1 //Four level mindata tree
+    )
+  )
+);
+
+TEST_P(DataTreeTest_ResizeByTraversing_P, StructureIsValid) {
+  GrowTree(tree.get(), numberOfLeavesToAdd);
+  EXPECT_IS_LEFTMAXDATA_TREE(tree->key());
+}
+
+TEST_P(DataTreeTest_ResizeByTraversing_P, NumBytesIsCorrect) {
+  GrowTree(tree.get(), numberOfLeavesToAdd);
+  // tree->numLeaves() only goes down the right border nodes and expects the tree to be a left max data tree.
+  // This is what the StructureIsValid test case is for.
+  EXPECT_EQ(newNumberOfLeaves, tree->numLeaves());
+}
+
+TEST_P(DataTreeTest_ResizeByTraversing_P, DepthFlagsAreCorrect) {
+  GrowTree(tree.get(), numberOfLeavesToAdd);
+  uint32_t depth = ceil(log(newNumberOfLeaves)/log(DataTreeTest_ResizeByTraversing::LAYOUT.maxChildrenPerInnerNode()));
+  CHECK_DEPTH(depth, tree->key());
+}
+
+TEST_P(DataTreeTest_ResizeByTraversing_P, KeyDoesntChange) {
+  Key key = tree->key();
+  tree->flush();
+  GrowTree(tree.get(), numberOfLeavesToAdd);
+  EXPECT_EQ(key, tree->key());
+}
+
+TEST_P(DataTreeTest_ResizeByTraversing_P, DataStaysIntact) {
+  uint32_t oldNumberOfLeaves = std::max(1u, ceilDivision(tree->numStoredBytes(), nodeStore->layout().maxBytesPerLeaf()));
+  TwoLevelDataFixture data(nodeStore, TwoLevelDataFixture::SizePolicy::Unchanged);
+  Key key = tree->key();
+  tree.reset();
+  data.FillInto(nodeStore->load(key).get());
+
+  GrowTree(key, newNumberOfLeaves);
+
+  data.EXPECT_DATA_CORRECT(nodeStore->load(key).get(), oldNumberOfLeaves, oldLastLeafSize);
+}
diff --git a/test/implementations/onblocks/utils/CeilLogTest.cpp b/test/implementations/onblocks/utils/CeilLogTest.cpp
new file mode 100644
index 00000000..4851da39
--- /dev/null
+++ b/test/implementations/onblocks/utils/CeilLogTest.cpp
@@ -0,0 +1,32 @@
+#include <google/gtest/gtest.h>
+#include "../../../../implementations/onblocks/utils/Math.h"
+
+#include <limits>
+
+using namespace blobstore::onblocks::utils;
+using ::testing::Test;
+using std::numeric_limits;
+
+class CeilLogTest: public Test {};
+
+TEST_F(CeilLogTest, Log3_0) {
+ EXPECT_EQ(0, ceilLog(3, 0));
+}
+
+TEST_F(CeilLogTest, Log3_1) {
+ EXPECT_EQ(0, ceilLog(3, 1));
+}
+
+TEST_F(CeilLogTest, Log3_2) {
+ EXPECT_EQ(1, ceilLog(3, 2));
+}
+
+TEST_F(CeilLogTest, Log3_3) {
+ EXPECT_EQ(1, ceilLog(3, 3));
+}
+
+TEST_F(CeilLogTest, Log3_4) {
+ EXPECT_EQ(2, ceilLog(3, 4));
+}
+
+//TODO ...