ACRONIS Backup & Recovery 10 Advanced Server User's Guide download pdf (Page 160)

go back in the archive) is 8 weeks. Tape rotation for the second case includes 128 daily sessions, i.e. it

allows the roll-back period equal 64 days. The roll-back period is always half the number of sessions.

Each additional level doubles not only the number of sessions but also the oldest backup age.

Let’s return to the analyzed case described in the Case to analyze (p. 152) section, and suppose the

ToH settings are the following:

• Schedule: Start the task every 1 day at 11:00 PM. Repeat once.

• Number of levels: 5

The Tower of Hanoi scheme with five levels ensures that the roll-back period is 8 days. Let’s designate

the backups of the levels with numbers from 1 to 5 by letters A, B, C, D, and E respectively. Then the

rotation template for the backup sequence in the archive is the following: E-A-B-A-C-A-B-A-D-A-B-A-C-

A-B-A. In the five-level ToH scheme all the backups on the 1st level (A) are incremental, on the 5th

level (E) – full, and other backups on levels 2, 3, and 4 (B, C, and D) are differential.

Tape rotation for the ToH scheme substantially depends on the tape options, whose default settings

do not always provide optimal usage of tapes and the whole tape library.

The goal is to choose the tape options requiring the minimal number of tapes in the rotation.

There are analyzed examples showing how the ToH scheme can be combined with different tape

options in the following sections:

• ToH Example 1 (p. 160). The Use a separate tape set option is selected. All the Always use a free

tape options are cleared. It requires 5 tapes in rotation.

• ToH Example 2 (p. 161). The Use a separate tape set option is selected. The Always use a free

tape: For each full backup option is selected. The other Always use a free tape options are

cleared. It requires 4 tapes in rotation.

• ToH Example 3 (p. 162). The Use a separate tape set option is selected. All the Always use a free

tape options are selected. It requires 7 tapes in rotation.

ToH Example 2 requires 4 tapes, which is the minimum for the case. So its tape options settings are

the best in comparison with options for other examples.

ToH Example 1

Suppose, the backup plan has the following tape options:

• the Use a separate tape set option is selected

• the Always use a free tape: For each full backup option is cleared

• the Always use a free tape: For each incremental backup option is cleared

• the Always use a free tape: For each differential backup option is cleared.

The figure below shows the tapes’ usage for the ToH scheme combined with the above mentioned

tape options. The recurring part of the scheme contains sixteen backup sessions. The figure displays

the backup archive state at the moment when the 17th session is finished.

1 2 ... 155 156 157 158 159 160 161 162 163 164 165 ... 403 404

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ACRONIS Backup & Recovery 10 Advanced Server User's Guide Page 160