Backup Rotation Methods
GRANDFATHER-FATHER-SON BACKUP STRATEGY
GFS (grandfather, father, son) is a tape rotation strategy. GFS simplifies tape handling by organizing rotation into daily, weekly, and monthly backup tapes. You can also create Custom backup jobs that use the GFS strategy.
LAN administrators consider GFS one of the simplest and most effective tape rotation strategies.
The GFS tape rotation strategy provides several benefits:
What is GFS?
The GFS tape rotation strategy is based on a 7-day schedule (Sunday through Saturday), in which you create at least one full backup each week. The rest of that week's backups can be full or differential. (A differential backup saves only the files that changed since the last full backup.)
Regardless of the number of full backups you create during the week, the LAST full backup of the week is considered the WEEKLY backup. You can reuse (recycle) the DAILY and WEEKLY backup tapes or take them offsite for permanent storage. For a discussion of when to reuse tapes, see Tape Recycling later in this document.
Here are some examples of weekly backup schedules:
*Diff = Differential backup
In GFS terminology, the DAILY backup is the son and the FULL WEEKLY backup is the father. The last full backup of each month is considered the MONTHLY backup. In GFS terminology, it is the grandfather. The MONTHLY backup is always permanent--it cannot be reused. It's a good idea to store permanent tapes offsite.
The following is an example of a typical backup schedule.
|Tape 1||Tape 2||Tape 3||Tape 4||Tape 5|
|Tape 1||Tape 2||Tape 3||Tape 4||Tape 6|
|Tape 1||Tape 2||Tape 3||Tape 4||Tape 7|
|Tape 1||Tape 2||Tape 3||Tape 4||Tape 8|
* Diff=Differential backup
By default, backup recycles (reuses) DAILY tapes after the fourth daily backup. (In the previous example, notice how tapes 1 through 4 were reused each Monday through Thursday.) This four day cycle lets you restore a file to the state it was in on any of those four specific days. By default, backup recycles WEEKLY backup tapes after the fifth full weekly backup.
The previous example assumes that you've used the default tape recycle for a backup. In this case, a full year of backups would require 22 tapes: 4 DAILY, 5 WEEKLY, and 13 MONTHLY. Of course, this number can increase when tapes are retired at the end of their useful life, or if the tape recycle is increased.
Please note, in an effort to keep costs reasonable, all drop offs and pick ups are scheduled.
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