Veritas-bu

[Veritas-bu] Retention Period Question

2006-05-16 16:40:33
Subject: [Veritas-bu] Retention Period Question
From: wtsmith AT maine DOT edu (Wayne T Smith)
Date: Tue, 16 May 2006 16:40:33 -0400
Your retentions are *not* OK.   

Let's say you need to restore from an incremental from 60 days ago.  The 
Full that goes with that incremental might may have been done 4 weeks 
before that.  So the retention of your Full is OK, but in order to do a 
complete restore to 60 days ago, your incrementals from 60 days ago back 
through to its full must be available.  You must increase the retentions 
of your incrementals by 4 weeks (I may give best tape drive utilization 
to simply go to 90 days).

With that said, you should be aware of potential problems with this 
system, a system which must be *very* reliable, IMHO:

* A restore from data close to the next Full, will have *many* parts 
(Full plus up to 27 incrementals).  Are your differential backups that 
much different from cumulative backups?  I recommend forgetting 
differential backups and using only full plus cumulative incrementals.  
With cumulative incrementals, there is very little difference between a 
restore soon after a full and one just before the next full.

* Problems backing up *will* happen from time to time.   If you "miss" a 
full backup, is it retried the next day (this is usually possible with 
NetBackup and calendar scheduling)?  If not, you run the risk that the 
incrementals run after the failed full will be based a full that will 
expire before your guarantee.

* I'm a firm believer in "you can't have too many backups".   Monthly 
fulls and differential incrementals just don't give me enough copies of 
data to make me at all comfortable with your set up.  Please consider 
more frequent full backups and cumulative incrementals.  Yes, it means a 
more storage for catalog and data, but it means you have alternatives 
when bad things happen ... and they will.

Hope this helps!

cheers, wayne

DLew97 wrote, in part,  on 5/16/2006 9:14 AM:
> Our corporate retention policy for data is 60days guaranteed.
>  
> How should I setup my retention periods?
>  
> Currently we run a FULL every 4 weeks and a Differential Incremental 
> every day.
>  
> I have 60 days set for the incremental and 90 days set for the full.  
> I am not sure if this setting is correct.  I need to guarantee 60 days 
> of data at all times.  I am afraid that the earlier FULL is needed to 
> do a restoration if the the file has not been picked up by the 
> incrementals.
>  
> Any suggestions?
>
> -- 
> DLew97