Copyright © Acronis, Inc., 2000-2010
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incremental backups on first level (A) - to gain time and storage savings for the most frequent
backup operations; but data recovery from such backups takes longer because it generally
requires access to three backups
full backups on the last level (E for five-level pattern) - the rarest backups in the scheme, take
more time and occupy more space in storage
differential backups on all intermediate levels (B, C and D for five-level pattern)
the pattern starts with a full backup since the very first backup cannot be incremental
the scheme forces every backup level to keep only the most recent backup, other backups from
the level have to be deleted; however backup deletion is postponed in cases where the backup is
a base for another incremental or differential one
an old backup on a level is kept until a new backup has been successfully created on the level.
The table shows the pattern for the five-level backup scheme. The pattern consists of 16 sessions.
As a result of using incremental and differential backups the situation may arise when an old backup
deletion must be postponed as it still is a base for other backups. The table below indicates the case
when deletion of full backup (E) created at session 1 is postponed at session 17 until session 25
because the differential backup (D) created at session 9 is still actual. In the table all cells with
deleted backups are grayed out:
Differential backup (D) created at session 9 will be deleted at session 25 after creation of a new
differential backup is completed. This way, a backup archive created in accordance with the Tower of
Hanoi scheme by Acronis sometimes includes up to two additional backups over the classical
implementation of the scheme.
For information about using Tower of Hanoi for tape libraries, see Using the Tower of Hanoi tape
rotation scheme (p. 149).
2.7
Retention rules
The backups produced by a backup plan make an archive. The two retention rules described in this
section enable you to limit the archive size and set the lifetime (retention period) of the backups.
