ADSM-L

Re: Diskpool volume sizing

2005-12-03 13:57:39
Subject: Re: Diskpool volume sizing
From: Roger Deschner <rogerd AT UIC DOT EDU>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Sat, 3 Dec 2005 12:57:35 -0600
100gb is still way too small.

Your basic problem is that every day you will have 1TB of data arriving,
and you've got to put it somewhere. What you want to avoid is having
anything in your TSM server that will slow down the backup. The optimal
size is, of course, 1TB. This figure comes from the TSM Administrator's
Guide.

The key number is the ratio of data backed up daily to disk pool size.
1:1 is ideal. You can survive on 2:1 or even 3:1. But you'll be in a bad
way at 10:1 (100gb diskpool) and it probably won't work at all at 100:1
(10gb).

What this depends on is the net bandwidth of your migration facilities.
That is, how many tape drives do you have, how long can you afford to
keep them tied up, what kind of daily schedule you want to establish for
backup - migration - expiration - DBbackup. And do you want to risk
having a time period within the day when restores are impossible because
the tape drives are all occupied doing migration?

Another benefit of a larger disk storage pool size, especially if you
turn on storage pool cacheing, is very fast restores. If your Exchange
server must be completely restored, you could do it mostly from disk at
network speed, with no delays for tape mounts. (There is a cost here,
though: Disk storage pool cacheing will make your TSM database larger.)

There are lots of options here, but you should start from the premise
that the ideal diskpool size is a full day's worth of backed up data.
Reduce that as budget dictates and as you find you can migrate more than
once daily. But disks are cheap. 100gb is way too small - you'll be
migrating 10 times per day, and if something interrupts migration, such
as a client restore, you could fall behind on migration and backups will
stop. Also, if you migrate that often, you'll wear out your tapes. In
general, more disk space is better, and even more is even better.

Roger Deschner      University of Illinois at Chicago     rogerd AT uic DOT edu


On Fri, 2 Dec 2005, Kurt Beyers wrote:

>Hi,
>
>This size was mentioned during a discussion with an IBM consultant. There is 
>no tech note or something. If other users have other findings, they are 
>welcome of course.
>
>Kurt
>
>________________________________
>
>From: ADSM: Dist Stor Manager on behalf of Henrik Wahlstedt
>Sent: Fri 2/12/2005 11:13
>To: ADSM-L AT VM.MARIST DOT EDU
>Subject: Re: [ADSM-L] Diskpool volume sizing
>
>
>
>Hi,
>
>Where did you found that note about 'optimal' size. And what is the
>statement based of?
>
>//Henrik
>
>-----Original Message-----
>From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
>Kurt Beyers
>Sent: den 2 december 2005 11:05
>To: ADSM-L AT VM.MARIST DOT EDU
>Subject: Re: Diskpool volume sizing
>
>Hi,
>
>A maximum 'optimal' size for a disk volume would be 100GB. And don't
>forget to add 1 MB for the metadata that TSM writes in the disk volume.
>
>regards,
>Kurt
>
>
>________________________________
>
>From: ADSM: Dist Stor Manager on behalf of Pretorius Louw
><louw AT sun.ac DOT za>
>Sent: Fri 2/12/2005 11:03
>To: ADSM-L AT VM.MARIST DOT EDU
>Subject: [ADSM-L] Diskpool volume sizing
>
>
>
>Hi all,
>
>We're creating a diskpool for our Exchange-backups of about 1TB and was
>wondering if an volume size of 10GB is correct or if we should be
>looking at larger volumes.
>
>Regards
>
>Louw Pretorius
>
>_______________________________
>
>Informasie Tegnologie
>
>Stellenbosch Universiteit
>
>
>
>There are only 10 kinds of people in the world: Those who understand
>binary and those who don't
>
>
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