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backup policy/plan starts on Wednesday and full backups should be created on every fourth Friday,
on Wednesday the first backup will be full instead of an incremental one.
There are analyzed examples showing how the GFS scheme can be combined with different tape
options in the following sections:
GFS Example 1 (p. 139). The
Use a separate tape set
option is selected. All the
Always use a free
tape
options are cleared. It requires 25 tapes in rotation.
GFS Example 2 (p. 142). The
Use a separate tape set
option is selected. The
Always use a free
tape: For each full backup
option is selected. Other
Always use a free tape
options are cleared.
It requires 16 tapes in rotation.
GFS Example 3 (p. 144). The
Use a separate tape set
option is selected. All the
Always use a free
tape
options are selected. It requires 28 tapes in rotation.
These examples demonstrate how the number of tapes required for automated rotation depends on
the tape options. If a tape library does not have enough tapes for automated rotation, the
Tasks
Need Interaction
window will sometimes ask you to load a free tape into the library.
GFS 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.
Imagine the first backup operation is scheduled on Friday 1st of January. On that day at 11:00 PM the
first full backup (320 Gb on the tape whose size is 400 Gb) is created. As the
Use a separate tape set
option is selected, the currently mounted tape is ejected (if it is not a free tape). Then a free tape is
loaded especially for backing up the data. The tape is marked with number 01 in the figure below. In
accordance with the legend described in the Case to analyze (p. 138) section, the full data backup is
displayed as an orange rectangle in the figure.
The specified GFS backup scheme settings force the data to be backed up on
Workdays
only, so the
next backup is created at the same time (
11:00 PM
) on Monday 4th of January. This backup is an
incremental one (16 Gb) that is written onto the same tape 01, because the
Always use a free tape:
For each incremental backup
option is cleared. The backup is drawn as a green rectangle in the
figure.
The next three incremental backups are written onto tape 01 on 5th, 6th and 7th of January. As a
result the free space on the tape is only 16 Gb at the moment.
On 8th of January the data differential backup (40 Gb) is recorded onto the same tape 01, as the
Always use a free tape: For each differential backup
option is cleared. However the tape reached
the end after the first 16 Gb of the backup is written. Then the tape is dismounted and ejected from
the drive into a slot by the loader. Further, a free tape is loaded into the same drive and mounted,
and then the backup (last 24 Gb) is continued onto the beginning of the new tape.
