ACRONIS Backup & Recovery 10 Advanced Server Virtual Edition User's Guide download pdf (Page 209)

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. 166), weekly (p. 168), or monthly (p. 170) 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.

A cleanup mechanism ensures that only the most recent backups of each level are kept. Here is how

the archive looks on day 8, a day before creating a new full backup.

1 2 3 4 5 6 7 8

4 1 2 1 3 1 2 1

The scheme allows for efficient data storage: more backups accumulate toward the current time.

Having four backups, we could recover data as of today, yesterday, half a week, or a week ago.

1 2 ... 204 205 206 207 208 209 210 211 212 213 214 ... 388 389

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ACRONIS Backup & Recovery 10 Advanced Server Virtual Edition User's Guide Page 209