Tracking block-level changes using snapshots

Writes to blocks of a protected storage volume that occur between the beginning of a prior backup interval and the beginning of a current backup interval are tracked using a first snapshot that is maintained through the current backup interval. At the beginning of the current backup interval, a second snapshot is generated. Blocks that are indicated by a dirty block list of the first snapshot as having been changed are read from the snapshot volume for the second snapshot and copied to a backup storage volume. For the next backup interval, the second snapshot or alternatively, a newly generated third snapshot, is used to track writes to blocks of a protected storage volume that occur between the beginning of the current backup interval and the beginning of a next backup interval.