206 Copyright © Acronis, Inc., 2000-2010A new level 3 differential backup has not yet been created, so the backup of day five is still stored.Since it depends on the full backup of day one, that backup is available as well. This enables us to goas far back as 11 days, which is the best-case scenario.The following day, however, a new third-level differential backup is created, and the old full backup isdeleted.1 2 3 4 5 6 7 8 9 10 11 12 134 1 2 1 3 1 2 1 4 1 2 1 3This gives us only a four day recovery interval, which turns out to be the worst-case scenario.On day 14, the interval is five days. It increases on subsequent days before decreasing again, and soon.1 2 3 4 5 6 7 8 9 10 11 12 13 144 1 2 1 3 1 2 1 4 1 2 1 3 1The roll-back period shows how many days we are guaranteed to have even in the worst case. For afour-level scheme, it is four days.6.2.9.6 Custom backup schemeAt a glance Custom schedule and conditions for backups of each type Custom schedule and retention rulesParametersParameter MeaningFull backup Specifies on what schedule and under which conditions to perform a full backup.For example, the full backup can be set up to run every Sunday at 1:00 AM assoon as all users are logged off.Incremental Specifies on what schedule and under which conditions to perform anincremental backup.If the archive contains no backups at the time of the task run, a full backup iscreated instead of the incremental backup.Differential Specifies on what schedule and under which conditions to perform a differentialbackup.If the archive contains no full backups at the time of the task run, a full backup iscreated instead of the differential backup.Clean up archive Specifies how to get rid of old backups: either to apply retention rules (p. 39)regularly or clean up the archive during a backup when the destination locationruns out of space.By default, the retention rules are not specified, which means older backups willnot be deleted automatically.Using retention rulesSpecify the retention rules and when to apply them.This setting is recommended for backup destinations such as shared folders orcentralized vaults.When there is insufficient space while backing up
