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StorageExpress(TM) System: Grandfather-Father-Son Backup Strategy
STORAGEEXPRESS(TM) SYSTEM: GRANDFATHER-FATHER-SON BACKUP STRATEGY
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.
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.
* 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.
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
--- --- ---- --- ---- --- ---
Diff Diff Diff Full 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
SUN MON TUES WED THUR 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 TUES WED THUR 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. For a
discussion of tape retirement, see document 6720.
Central Console's Tape Recycle window (available when you choose
Advanced Options from the Streamlined Backup and Settings window) lets
you change the 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 TUES WED THUR 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.
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