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This figure demonstrates that the
GFS Example 2
tape rotation scheme is more suitable for the case
than
GFS Example 1
. The advantages of the
GFS Example 2
tape rotation scheme for the analyzed
case are the following:
it uses 16 tapes instead of 25
a data recovery task requires one (25%) or two (75%) tapes
data recovery from a full backup requires only one tape that makes the data recovery from an
incremental or differential backup faster.
GFS Example 3
Imagine 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 selected
the
Always use a free tape: For each incremental backup
option is selected
the
Always use a free tape: For each differential backup
option is selected.
These options define the tape rotation scheme that is classical for GFS. The figure shows the
beginning of the rotation scheme that uses 8 tapes for daily backups, 6 tapes for weekly backups and
13 tapes for monthly backups (since there are 13 four-week cycles in a year) for the analyzed case.
And one tape is required for the next backup. In total this rotation scheme, combined with the
options requires 28 tapes.
To recover the data only one tape is required for a full backup, two tapes for a differential backup,
and two or three tapes for an incremental backup.
This scheme has the following advantages:
access to any full backup requires only one tape
backup deletion frees a tape so it can be reused.
