User Guide

Even though it is possible to use GFS to create such an archive, the Custom scheme is more flexible in

this situation.

6.2.9.5. Tower of Hanoi scheme

At a glance

• Up to 16 levels of full, differential, and incremental backups

• Next-level backups are twice as rare as previous-level backups

• One backup of each level is stored at a time

• Higher density of more recent backups

Parameters

You can set up the following parameters of a Tower of Hanoi scheme.

Schedule Set up a daily (p. 81), weekly (p. 83), or monthly (p. 85) schedule. Setting up

schedule parameters allows creating simple schedules (example of a simple

daily schedule: a backup task will be run every 1 day at 10 AM) as well as more

complex schedules (example of a complex daily schedule: a task will be run

every 3 days, starting from January 15. During the specified days the task will

be repeated every 2 hours from 10 AM to 10 PM). Thus, complex schedules

specify the sessions on which the scheme should run. In the discussion below,

"days" can be replaced with "scheduled sessions".

Number of levels Select from 2 to 16 backup levels. See the example stated below for details.

Roll-back period

The guaranteed number of sessions that one can go back in the archive at any

time. Calculated automatically, depending on the schedule parameters and the

numbers of levels you select. See the example below for details.

Example

Schedule parameters are set as follows

• Recur: Every 1 day

• Frequency: Once at 6 PM

Number of levels: 4

This is how the first 14 days (or 14 sessions) of this scheme's schedule look. Shaded numbers denote

backup levels.

1 2 3 4 5 6 7 8 9 10 11 12 13 14

4 1 2 1 3 1 2 1 4 1 2 1 3 1

Backups of different levels have different types:

• Last-level (in this case, level 4) backups are full;

• Backups of intermediate levels (2, 3) are differential;

• First-level (1) backups are incremental.