Copyright © Acronis, Inc., 2000-2010
143
.
Using the Grandfather-Father-Son tape rotation scheme
Tape rotation for the GFS backup scheme is substantially defined by the tape options specified for
the backup policy/plan to be created.
Assume the GFS settings are the following:
Start backup at:
11:00:00 PM
Back up on: Workdays
Weekly/Monthly: Friday
Keep backups:
Daily: 2 weeks; Weekly: 2 months; Monthly: 1 year
.
The main goal is to achieve full automation of tape rotation for these settings.
Keep in mind that a monthly backup is full, a weekly backup is differential, and a daily backup is
incremental in this implementation of the GFS scheme. The first backup is always full. So if the
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. 143). 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. 146). 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. 148). 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. 142) 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:
