RE: Write cache for a SAN

Jared,

We actually suffered a "SANtastrophe" about three years ago, in a real life circumstance that was quite similar to the one you describe.

The way the story was told to me, the SAN frame has a redundant power supply, and one of the two power supplies went bad, and the unit phoned home. EMC tech shows up w/ replacement power supply in hand, a few hours later. (This is the way it's supposed to work, right?) Well, apparently, he pulled the good power supply, rather than the bad power supply....leaving the frame to come crashing down w/ no power.....oops.....

36 hours, and about 2.5TB restored from tape later, and we were back in business.

This really is the exception, though, and not the rule. I don't think disabling write caching is the right move. Ultimately, at some point, you have to have some faith in the hardware you've got and the people you work with.

-Mark

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Mark J. Bobak
Senior Database Administrator, System & Product Technologies ProQuest
789 E. Eisenhower, Parkway, P.O. Box 1346 Ann Arbor MI 48106-1346
+1.734.997.4059 or +1.800.521.0600 x 4059 mark.bobak_at_proquest.com<mailto:mark.bobak_at_il.proquest.com> www.proquest.com<http://www.proquest.com> www.csa.com<http://www.csa.com>

ProQuest...Start here.

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Jared Still Sent: Monday, November 03, 2008 2:09 PM
To: dofreeman_at_state.pa.us
Cc: Oracle-L Freelists
Subject: Re: Write cache for a SAN

On Mon, Nov 3, 2008 at 7:19 AM, Freeman, Donald <dofreeman_at_state.pa.us<mailto:dofreeman_at_state.pa.us>> wrote: We don't disable it. The SAN manufacturers have made this as bullet proof as possible.

Guess what happens when the storage vendor sends out a tech to replace batteries (the batteries that ensure the write cache stays put), and the tech can't be bothered to follow instructions?

What do you think might happen to the write cache?

I'm not saying that the write cache should be disabled, but you need to ensure that the folks that maintain the HW actually know what they are doing.

Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

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http://www.freelists.org/webpage/oracle-l Received on Mon Nov 03 2008 - 13:29:10 CST