File system image transfer

The invention provides a method and system for duplicating all or part of a file system while maintaining consistent copies of the file system. The file server maintains a set of snapshots, each indicating a set of storage blocks making up a consistent copy of the file system as it was at a known time. Each snapshot can be used for a purpose other than maintaining the coherency of the file system, such as duplicating or transferring a backup copy of the file system to a destination storage medium. In a preferred embodiment, the snapshots can be manipulated to identify sets of storage blocks in the file system for incremental backup or copying, or to provide a file system backup that is both complete and relatively inexpensive. Also in a preferred embodiment, shadow snapshots can be maintained, with a shadow snapshot including a set of member storage blocks that formed a consistent file system other than an active file system, with a set of selected member storage blocks removed from the consistent file system.