The disk storage pools need to be RAID-1+. It's "other people's data"
and you are responsible for it, from the moment it is backed up from
their client systems. As you have discovered, performance is not good
with anything other than RAID-1.

The Database and the Log also need to be RAID-1. (Mirrored by TSM or the
OS or something) I tried striping (RAID-10, in effect) my TSM database,
and caused a performance disaster that I had to back out of fast. The
Log might survive RAID-5 without any performance penalty; I haven't
tried it. Just remember that the Log is strictly write-only until
disaster recovery becomes necessary.

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


On Sun, 28 Jul 2002, Seay, Paul wrote:

>There is one caveat Mark.
>
>If the loss of a backup is a critical failure to an application, then you
>must Raid-1 or Raid-5 the pool.  I have applications that take processing
>cycle backups several times throughout their processing cycle.  I also have
>servers that have to have the same backup cycle.  So, an unprotected
>diskpool is not a black or white answer to solving a performance problem.
>
>However, you are correct, RAID-5 is going to perform like crap for disk
>pools unless you have ESS disk which have a very large disk cache on the
>front and the RAID-5 turns into RAID-3 (no reads before writes because it is
>always a full stripe write).
>
>Paul D. Seay, Jr.
>Technical Specialist
>Naptheon Inc.
>757-688-8180
>
>
>-----Original Message-----
>From: Mark Stapleton [mailto:stapleto AT BERBEE DOT COM]
>Sent: Sunday, July 28, 2002 1:46 AM
>To: ADSM-L AT VM.MARIST DOT EDU
>Subject: Re: diskpool performance
>
>
>From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU]On Behalf Of 
>Dirk
>Kastens
>> Seemed to be a faulty raid controller. We always used raid5 for TSM
>> volumes and never got any errors or bottlenecks. Of course, we use
>> different raids for stgpools and the database.
>
>A question: why are RAIDing your TSM diskpool? There's no need for
>redundancy in the diskpool, since the diskpool is not the mission-critical
>component of your backup system. It's the *tape* pool you need redundancy
>for, and that's what a copy pool is for.
>
>You *might* RAID 0 your diskpool, so that you stripe across the pool disks
>for a larger number of read/write heads, but there's nothing but unnecessary
>overhead when you RAID 5 it. The diskpool dies? You fix the pool, and you
>back up the files again the next night.
>
>--
>Mark Stapleton (stapleton AT berbee DOT com)
>Certified TSM consultant
>Certified AIX system engineer
>MCSE
>