Re: Miserable Disks
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: pythianbrinsmead@xxxxxxxxx
- Date: Thu, 25 May 2006 23:20:41 -0600
At 08:55 PM 5/25/2006, Mark Brinsmead wrote:
Oh, by the way, I happen to know the site that Wolfgang referred
to. It may amuse you to
know that this particular site (last time I heard from them, anyway)
was planning to deploy
about 15TB of *new* storage in their existing CX-700 disk array,
using 500GB SATA disks
in a RAID-5 configuration. I think Wolfgang knew of this plan --
perhaps he was just too
polite to point it out. ;-)
Yes, I knew of the plan. Actually it was put in place while I was
still there. I don't believe it is as bad as you make it out. It
allowed us to use RAID 10 on the smaller, faster disks in the CX700
for the production databases by moving all development and support
databases (~ 7 for each production database) to those big disks -
without management crying foul.
In my experience, bad sql, or bad plan choices (helped along by poor
sql) by the optimizer are more often the cause of poor performance
than database parameters, OS parameters, or the IO subsystem - unless
you made some very poor setup decisions. Case in point is the
situation I described earlier. We noticed the IO problem in
operations on the OS - backups, file copies - *not* in database
performance, even though the IO times were abysmal. The backup took
4+ hours instead of 10-20 minutes. Nor did we see a big boost in
database performance when the problem was resolved.
Regards
Wolfgang Breitling
Centrex Consulting Corporation
http://www.centrexcc.com
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