ADSM-L

Re: Mitigating Risk with TSM's incremental backups

2002-01-24 09:23:37
Subject: Re: Mitigating Risk with TSM's incremental backups
From: Bill Mansfield <WMansfield AT SOLUTIONTECHNOLOGY DOT COM>
Date: Thu, 24 Jan 2002 08:20:59 -0600
Justin,
TSM isn't really designed for a regular offsite rotation.  The intention is
to send the copy storagepool tape offsite each day, regardless of how full
it is.  You then perform offsite reclamation, which uses primary storage
pool tapes (or optical) to recombine the data from several partially full
offsite tapes *without recalling the offsite tape*.  This is the critical
issue in your question.  The new offsite tape (which might contain some of
today's backup data) is sent offsite.  After a brief period defined by
reusedelay in the copy stgpool definition (to cover the courier moving the
new tape offsite), the volume goes empty and can be recalled and turned
back into a scratch tape.

Given the low volume of data generation (1 GB/day) and the high capacity of
LTO tape (100 GB) this is going to cause what appears to be a lot of
reclamation activity, but the net effect should be that one tape goes
offsite and one tape comes back onsite every day.  Hope you have a library.

_____________________________
William Mansfield
Senior Consultant
Solution Technology, Inc




                    Justin Derrick
                    <jderrick@CANA       To:     ADSM-L AT VM.MARIST DOT EDU
                    DA.COM>              cc:
                    Sent by:             Subject:     Mitigating Risk with 
TSM's incremental backups
                    "ADSM: Dist
                    Stor Manager"
                    <ADSM-L AT VM DOT MAR
                    IST.EDU>


                    01/24/2002
                    07:05 AM
                    Please respond
                    to "ADSM: Dist
                    Stor Manager"






I've been using TSM for quite a few years on AIX, and surprisingly, this
issue hasn't come up before.

My customer is using TSM in conjunction with Content Manager OnDemand.  The
config looks like this:

AIX 4.3.3 on H70
OnDemand, DB2, TSM
Data is cached on disk (by OnDemand, not TSM), and also copied to Optical
(a la 3995), then backed up to LTO.
They are currently a very low-volume shop, adding under 1GB a day to the
TSM system.

The question raised to which I didn't have a good answer was:

If we take a non-full LTO offsite for disaster recovery purposes, then
bring it back onsite as part of regular rotation, a vulnerability is
created.  If the tape is on site when a disaster occurs (which would always
be the case since their courier only delivers once a day), not only is that
day's information lost, but all the previous days of incrementals
previously written to the tape are destroyed as well.

I know we could keep multiple copypools in the chain, but it seems like an
expensive solution to a simple problem.

The immediate solution would be to create new 'full' backups of the
contents of the optical jukebox every day, and take them offsite.  While
this would actually be feasible in the short term (given their low growth)
it would quickly become unmanagible in the future.

Is the solution to simply buy enough tapes so that you simply send one tape
a day offsite for as long as possible, then perform large reclaimation once
every 'long as possible'?  This sounds like it's within the realm of the
DRM, which I'm woefully inexperienced with.  Any advice, direction, etc.
would be greatly appreciated.

-JD.
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