Patent attributes
Techniques for reducing overheads of primary storage while transferring modified data are described. According to one embodiment, in response to a request at a primary storage for a backup of a plurality of data blocks, a snapshot of the plurality of data blocks is captured, wherein the snapshot represents a consistent state of the plurality of data blocks. Then a set of data block of the captured snapshot that are to be copied to a secondary storage is identified and the identified set of data blocks are transferred to a secondary storage over a network. In response to receiving data to be written to a first data block at the first primary storage during the transfer, current contents of the first data block is preserved if the first data block is in identified set of data blocks, and the received data is committed to the first data block.