Net Services of Amarillo


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.

Why GFS?

LAN administrators consider GFS one of the simplest and most effective tape rotation strategies.

The GFS tape rotation strategy provides several benefits:

  • It protects your data with a minimum number of tapes (normally, only one or two tapes are required to restore a file server), rotating some tapes and archiving others, so you can easily restore one file or an entire file server.
  • It reduces wear and tear on tapes and tape heads.
  • It provides a systematic approach to tape storage that ensures the highest possible protection for your data and gives you an easy way to locate stored files. This makes restoring directories and volumes fast and easy.

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:

EXAMPLE 1

SUN MON TUES WED THUR FRI SAT
None Diff Diff Diff Diff FULL None
*WEEKLY*            

EXAMPLE 2

SUN MON TUES WED THUR FRI SAT
None Diff Diff Diff Diff Diff FULL
*WEEKLY*            

*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.

MONTH 1

6 None
SUN MON TUES WED THUR FRI SAT
1 2 3 4 5 6 7
None Diff* Diff Diff Diff F-W** None
Tape 1 Tape 2 Tape 3 Tape 4 Tape 5
8 9 10 11 12 13 14
None Diff* Diff Diff Diff F-W** None
  Tape 1 Tape 2 Tape 3 Tape 4 Tape 6  
15 16 17 18 19 20 21
None Diff* Diff Diff Diff F-W** None
  Tape 1 Tape 2 Tape 3 Tape 4 Tape 7  
22 23 24 25 26 27 28
None Diff* Diff Diff Diff F-W** None
  Tape 1 Tape 2 Tape 3 Tape 4 Tape 8  
             

* Diff=Differential backup

**F-W=Full WEEKLY

Tape recycling

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.