ACRONIS Backup & Recovery 10 Advanced Server User's Guide download pdf (Page 153)

 compression level specified for backing up the data

 tape rotation scheme ( frequency of backups, retention rules)

 tape-append options

 requirements to support off-site tape cartridge archives.

There is no common formula to calculate a number of tapes required in all possible combinations of

above listed considerations. But the general way to get a number of tapes for a case includes the

following steps:

1. Draw (or write) a chain of backups until the first backup can be deleted

2. Take into account the tape-append options, the chain might be sectioned onto tape sets

3. Calculate the number of tapes in each tape set

4. The sum of the calculated values gives the total number of tapes required for the case.

Tape planning: Example 1

Imagine the case with the following features:

 full backup size is F_GB

 average size of incremental backups is I_GB

 average size of differential backups is D_GB

 compression level provides CL average reduction coefficient

 selected tape rotation scheme is Tower of Hanoi with four levels

 tape options are the following:

 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

 tape size is T_GB.

The Tower of Hanoi scheme with four levels (A, B, C, and D) specifies the following line of backups on

the tapes before the first backup will be deleted: D (full), A, B, A, C, A, B, A, D, A, B, A, C. The specified

tape options do not require using a free tape for any backup, so the backup line will be automatically

split and continued on a new tape when the end of the current tape is reached. There is one tape set

to calculate.

Total number of required tapes = round up ((2*F_GB + 6*I_GB + 5*D_GB) * CL / T_GB) + 1.

The above described ToH Example 1 (p. 149) is based on the five-level Tower of Hanoi backup

scheme with the same tape options. Its backup line was the following: E (full), A, B, A, C, A, B, A, D, A,

B, A, C, A, B, A, E, A, B, A, C, A, B, A, D.

Total number of required tapes = round up ((2*F_GB + 12*I_GB + 11*D_GB) * CL / T_GB) + 1 = round

up ( (2*320 + 12*16 + 11*40) * 1 / 400 ) + 1 = round up ( 3.18 ) + 1 = 5 (tapes).

Tape planning: Example 2

Imagine the case with the following features:

 full backup size is F_GB

 average size of incremental backups is I_GB

 average size of differential backups is D_GB

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ACRONIS Backup & Recovery 10 Advanced Server User's Guide Page 153