Systems and methods for performing sparse backups are disclosed. One method may involve: receiving information indicating unallocated extents from a file system that organizes data on a primary storage device; copying to a backup storage device data from extents of the primary storage device, where the unallocated extents indicated by the information are not copied; and for each of a plurality of copied extents, storing a mapping from an original extent on the primary storage device to a new extent on the backup storage device into which data stored in that original extent is copied. A backup volume that includes the data included in plurality of copied extents may be mounted, and the mapping may be used to translate accesses to the extents on the backup volume to extents on the backup storage device.