A temporary file is identified. The temporary file includes a data block containing a first file image. A determination is made whether the temporary block has been included in a previous snapshot. Responsive to receiving a modification of the temporary block that has been included in the previous snapshot, a modified first image is created. The modified image is stored in the original file block, and the original image is copied to a newly allocated block. The original first block is updated to include a reference to the second block.