What is GFS?
GFS (grandfather, father, son) is the tape rotation strategy used in the StorageExpress™ system's streamlined backup. 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.

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.

• It maximizes File Tracker use while keeping down the File Tracker's size.

The File Tracker is a database that stores information about every file on every backup tape created by the StorageExpress system (except Tape-to-go and Self-backups). This makes restoring directories and volumes fast and easy.

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	TUE	WED	THU	FRI	SAT
----	----	----	----	----	----	----
None	Diff*	Diff	Diff	Diff	FULL	None

EXAMPLE 2

SUN	MON	TUE	WED	THU	FRI	SAT
----	----	----	----	----	----	----
Diff	Diff	Diff	Full	Diff	Diff	FULL

*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

SUN	MON	TUE	WED	THU	FRI	SAT
----	----	----	----	----	----	----
1	2	3	4	5	6	7
None	Diff*	Diff	Diff	Diff	F-WKLY**
	Tape 1	Tape 2	Tape 3	Tape 4	Tape 5
----	---	----	----	----	----	----
8	9	10	11	12	13	14
None	Diff	Diff	Diff	Diff	F-WKLY	None
	Tape 1	Tape 2	Tape 3	Tape 4	Tape 6
----	----	----	----	----	----	----
15	16	17	18	19	20	21
None	Diff	Diff	Diff	Diff	F-WKLY	None
	Tape 1	Tape 2	Tape 3	Tape 4	Tape 7
----	----	----	----	----	----	----
22	23	24	25	26	27	28
None	Diff	Diff	Diff	Diff	F-MTHLY	None
	Tape 1	Tape 2	Tape 3	Tape 4	Tape 8
----	----	----	----	----	----	----
29	30	31
None	Diff	Diff
	Tape 1	Tape 2
----	----	----

MONTH 2

SUN	MON	TUE	WED	THU	FRI	SAT
---	----	----	----	----	----	----
			1	2	3	4
			Diff	Diff	F-WKLY	None
			Tape 3	Tape 4	Tape 9
----	----	----	----	----	----	----
5	6	7	8	9	10	11
None	Diff	Diff	Diff	Diff	F-WKLY	None
	Tape 1	Tape 2	Tape 3	Tape 4	Tape 10
----	----	----	----	----	----	----

* Diff=Differential backup

**F-WKLY=Full WEEKLY

Tape recycling
By default, Streamlined 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, Streamlined backup recycles WEEKLY backup tapes after the fifth full weekly backup.

The previous example assumes that you've used the default Tape Recycle settings for a Streamlined backup. In this case, a full year of backups would require 21 tapes: 4 DAILY, 5 WEEKLY, and 12 MONTHLY. Of course, this number can increase when tapes are retired at the end of their useful life, or if the Tape Recycle setting is increased.

Central Console's Tape Recycle window (available when you choose Advanced Options from the Streamlined Backup and Settings window) lets you change the number of DAILY and WEEKLY tapes you'll use before recycling. You can increase the DAILY Tape Recycle setting to restore data from more individual days.

In the following example of an eight day recycle setting, you can restore a file to the state it was in on day 2 through day 11 (day 6 is included because it's a full weekly backup).

SUN	MON	TUE	WED	THU	FRI	SAT
----	----	----	----	----	----	----
1	2	3	4	5	6	7
None	Diff*	Diff	Diff	Diff	F-WKLY	None
	Tape 1	Tape 2	Tape 3	Tape 4	Tape 5
----	----	----	----	----	----	----
8	9	10	11	12	13	14
None	Diff	Diff	Diff	Diff	F-WKLY	None
	Tape 6	Tape 7	Tape 8	Tape 1	Tape 9
----	----	----	----	----	----	----
15	16	17	18	19	20	21
None	Diff	Diff	Diff	Diff	F-WKLY	None
	Tape 2	Tape 3	Tape 4	Tape 5	Tape 10
----	----	----	----	----	----	----

What if you don't use GFS?
If you don't use a tape rotation scheme, the File Tracker can quickly exceed the capacity of even the largest hard disk.

The File Tracker grows by 130 to 160 bytes for every backed-up file. When the StorageExpress™ system's hard disk reaches 80% of its capacity, it automatically prunes (deletes) the oldest file detail history. If the File Tracker has pruned data that you later want to restore, you'll have to use the slower Manual Restore option, or merge the tape back into the File Tracker. (Merging is the process of manually adding file detail history to the File Tracker database.)

You can stop File Tracker growth by purging old tapes from it periodically. When you purge a tape from the File Tracker database, all information about that tape's file detail history is deleted.

You can manually purge tapes from the File Tracker database by using the Purge button in the Central Console's Browse Tape Catalog menu. This can be time consuming, though.

The easiest way to prevent File Tracker overgrowth is to let the GFS tape rotation strategy manage the purging for you. GFS automatically purges the File Tracker database of the tape's file detail history when a tape is reused.

Avoid renaming or bulk-erasing tapes
When tapes are renamed or bulk-erased, the tape's file detail history remains in the File Tracker database. The File tracker database grows quickly.

Use the StorageExpress system to Quick-Erase or format the tape instead. It automatically deletes file detail history from the File Tracker database, slowing its growth.

This applies to:

StorageExpress™ Systems