This formula, while requiring less tape and time for the daily backups, will require more work on the part of the backup administrator to provide sane recovery after a filesystem crash. In the event of a Thursday crash, the administrator would have to restore the last FULL backup followed by the Monday, Tuesday and Wednesday backups.

In this diagram, each box, again, represents a single backup process. This illustrates a "differential" rotation scheme. Also, as before, each backup process could consist of one or more physical tapes. This plan uses the same weekly full system backup with the backup of files that have changed since the last full backup on a daily basis.

While this scheme takes up progressively more tape as each new day of the week passes, a recovery would only involve two tapes - the last FULL backup followed by the previous day's differential backup. Most backup administrators prefer this method as it simplifies recovery and most backups are done overnight.