Patent ID: 8417907

Claim:
A computer-readable storage medium having computer-executable instructions for causing a computer system to perform a method of synchronizing snapshots, said method comprising: accessing a first volume of data on a primary host, said first volume comprising a plurality of blocks of data including a first block of data; accessing a first snapshot of said first volume, said first snapshot comprising first metadata that points to blocks of data in said first volume that are unchanged since creation of said first snapshot, wherein said first metadata is included in said first snapshot instead of including in said first snapshot copies of said blocks of data that are unchanged since said creation of said first snapshot, said first snapshot comprising only copies of blocks of data that have been overwritten in said first volume since said creation of said first snapshot; prior to overwriting said first block of data in said first volume with changed data, writing said first block of data from said first volume to said first snapshot to produce a modified first snapshot; and synchronizing said modified first snapshot and a second snapshot of a second volume of data on a secondary host to produce a modified second snapshot, wherein said second volume comprises a replica of said first volume, said synchronizing comprising copying only a first portion of said modified first snapshot from said first snapshot to said second snapshot, said first portion comprising said first block of data.