Patent ID: 7444361

Claim:
A method, comprising: generating a persistent image of an active file system at a first point in time, wherein data is stored on a storage device of a storage system; comparing, at a later time than generating the persistent image, the active file system with the persistent image, by; if a block of data of the active file system is identical to the data in the persistent image, directing the active file system to refer to the persistent image for data of the file; if the block of data of the active file system is not identical to the data in the persistent image, directing the active file system to refer to the data of the active file system and comparing an inode of the active file system with an inode of the persistent image, and if the inode of the active file system and the inode of the persistent image are different, comparing the blocks pointed to by the inode of the active file system with the blocks pointed to by the inode of the persistent image in order to compare the active file system with the persistent image.