[Veritas-bu] Tape rotation - Best practice?

2004-09-21 12:00:49
Subject: [Veritas-bu] Tape rotation - Best practice?
From: wts AT maine DOT edu (Wayne T Smith)
Date: Tue, 21 Sep 2004 12:00:49 -0400
Heine Didriksen wrote, in part,  on 9/21/2004 3:35 AM:

> I am running Netbackup 5.0 on one W2K master and two tapelibraries, a 
> HP MSL5030 with two LTO1 and a Dell Powervault 136T with one LTO1.
> The Dell takes care of our exchange backup, while the HP takes the 
> filebackup.
> Currently, we have about 160GB of Exchange (full backup every night), 
> and around 1TB of filedata (Full backup once a week, and cum incr 
> every night.)
> We have 6 months retention on the full backups, and three on the 
> incrementals. Naturally, this generates a lot of tapes, and the bosses 
> have asked me to reconsider the tape rotation.
> So now I am looking for input from others. I have always thought that 
> six months is a lot, and I have never done restores from tapes more 
> that a month old.

I would think best practice is what gets the job done.  You've must 
determine your shop's expectation and need.  But cost enters  at some 
point, as you've seen, and perhaps legal or other obligations may enter 
your practice. 

So to use fewer tapes, you will need to keep less data, perhaps fewer 
images, than now.  For example, now you keep about 180 copies of your 
Exchange data base.

You've already decided (1) backups can't be kept forever and so are kept 
for 6 months, and (2) some backups may be discarded earlier than others 
and so cum incr are only kept for 3 months. 

Side note: You force different retention images to different tapes, do 
you not?  If you allow "multiple retentions per tape", then even though  
the cum incr are discarded from the catalog after 3 months, the space on 
tape is there for up to 6 months, since the tape for any cum incr may 
contain a full (6-month) image.

It helps to know your data a bit.  Can you obtain tape/catalog space 
savings by running cum incr in place of some or most of the fulls?  Can 
you save space by changing some or all of the cum incr to diff incr?  
Certainly there's a restore-side penalty, but what's the penalty cost 
and can it be tolerated?

Finally, you might encourage management to keep some percentage of the 
full backup images for a longer/shorter period of time than others.  
NetBackup makes it fairly easy to, for example, take daily fulls, but 
each week take a full that is kept longer, and each month take a full 
that is kept still longer, and each 6 months ... (you get the idea?).

There is an operational penalty for multiple retentions and relatively 
few tape drives: while you have a 6-month tape mounted, that drive will 
be unable to make any 6-week-retention backups.  Unless you have lots of 
extra time for backups, you may have to limit the total number of 
retentions you use.

Hope this helps, wayne

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