Hi Mark!
Correct me if I'm wrong, but you are saying, well, if a backup is lost due
to a disk failure, it's not a real problem, because you just tell TSM the
volume is gone and the files will be backed up again during the next backup
window.
In that's so, you overlook the following cases:
1) What if some backups are not performed on a daily bases? The impact on
missing a cycle is much bigger!
2) Missing backup pieces and correcting this in a TDP environment is a
tricky task. For instance, when you are using RMAN in your Oracle shop, you
will have a recovery catalog which is not in sync with TSM. It's not a very
easy task to get them in sync again...
Kindest regards,
Eric van Loon
KLM Royal Dutch Airlines


-----Original Message-----
From: Stapleton, Mark [mailto:mark.stapleton AT BERBEE DOT COM]
Sent: Wednesday, July 21, 2004 15:40
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: storage pool raid 1?


From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On
Behalf Of Daniel Sparrman
>I'd say that depends on the level of security the organisation
>requires.
>If the disks would crash before migration, it would mean
>you've just lost
>all the backup data since yesterday night. Would you like to
>go to your
>boss and inform him about that and explain to him that you saved 300$
>worth of disk?

True. However, this is an attempt to cover a double failure--the TSM
client and the TSM server disk. The only time I've seen a double failure
occur is during a complete system catastrophe--a server room fire, for
example--in which case the only redundancy that will save you is a
backup to tape that goes offsite.

>Also, if you dont migrate every morning, the loss of data
>could be alot bigger than just one nights backup.

Also true. However, the only systems I've set up (or seen) that don't
perform daily migrations to primary tape pools are disk farms that
*never* migrate to tape; in these cases, I can certainly see RAID5
redundancy as necessary.

In my experience, I see almost no case for fault tolerance in TSM-based
disk systems that normally perform a daily migration to a tape-based
primary storage pool. If a system crashing prior to migration worries
you, perform your migration as early in the day as you can after clients
finish running their backups to a cached disk pool.

--
Mark Stapleton


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