Patent ID: 7716184

Claim:
A method, comprising: a backup host receiving information indicating unallocated extents from a file system of a primary host that organizes data on a primary storage device, wherein each unallocated extent is an extent that is not currently allocated to a file or to metadata by the file system for storage of the file or the metadata; the backup host copying to a backup storage device data from extents of the primary storage device that correspond to the file system, wherein data from the unallocated extents indicated by the information is not copied; for each of a plurality of copied extents, the backup host storing a mapping identifying an original extent on the primary storage device and identifying a new extent on the backup storage device into which data stored in that original extent is copied; and the backup host using the mapping to translate accesses to extents on a backup volume that includes the data included in the plurality of copied extents to extents on the backup storage device; wherein each extent comprises a plurality of adjacent logical blocks specified by an address-length pair.