Re: What would you do with 8 disks?

  • From: Nuno Souto <dbvision@xxxxxxxxxxxx>
  • Date: Thu, 09 Apr 2009 12:36:13 +1000

Niall Litchfield wrote,on my timestamp of 9/04/2009 3:47 AM:
> good! Me, i'd try and get answers to the first set of questions and
> see if we couldn't use technology such as the raid controllers and asm
> to deal with the micromanagement of the second.

Indeed. The other thing I've found is that folks continue to think of RAID5 as only made up of 3 disks. It can have *at least* 3 disks but nothing stops one from striping more. I'm getting very acceptable results with 8 disks in a RAID5 stripe.

Perfectly acceptable to development/test requirements. Of course: not as the latest, fastest and brightest for a 10000000tps oltp benchmark. Then again, for that kind of numbers I've seen benchmarks with upwards of 500 disks, so that's a completely different ballgame.

Horses for courses. Don't even *dream* that an 8 disk system will have the same kind of performance, no matter what! RAID10 is great but again you won't see miracles with a stripe size of 4: you need a lot more than that to really get it screaming.

Bottom line: this is a limited setup with only 8 disks, so don't expect miracles out of the same config thoughts and strategy you'd use for 500 disks!

Given the limited disk setup, it probably is better to make a big RAID5 stripe volume. Logically partition it with the outer surfaces of the disks - the first 1/3 of the entire volume - dedicated to performance critical files like redos, undos and temp. The rest of the data can live in the remaining capacity with the last portion of the volume dedicated to storing software, programs, patches, new releases, etcetc.

Our development and test dbs are setup this way and the performance is quite acceptable for what it is. It has saved us heaps of $$$ as platinum-grade RAID10 stripes are hideously expensive. We reserve those to critical production, for max bang for buck.

Nuno Souto
in sunny Sydney, Australia


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