Message-ID: <4B4EAD76.9030305@postnewspapers.com.au>
Date: Thu, 14 Jan 2010 13:36:54 +0800
From: Craig Ringer <craig@postnewspapers.com.au>
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To: Robert Haas <robertmhaas@gmail.com>
CC: Eduardo Piombino <drakorg@gmail.com>,
 pgsql-performance@postgresql.org
Subject: Re: a heavy duty operation on an "unused" table kills my
 	server
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	<4B4D61DA.7080008@postnewspapers.com.au>	
	<e24c1d9d1001122303g1d4eea48h18bd73467d1fa8ec@mail.gmail.com>
	<603c8f071001130823l69804fe3m5c6fbb081c55c265@mail.gmail.com>
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Robert Haas wrote:

> I'm kind of surprised that there are disk I/O subsystems that are so
> bad that a single thread doing non-stop I/O can take down the whole
> server.  Is that normal?

No.

> Does it happen on non-Windows operating
> systems? 

Yes. My 3ware 8500-8 on a Debian Sarge box was so awful that launching a
terminal would go from a 1/4 second operation to a 5 minute operation
under heavy write load by one writer. I landed up having to modify the
driver to partially mitigate the issue, but a single user on the
terminal server performing any sort of heavy writing would still
absolutely nuke performance.

I landed up having dramatically better results by disabling the
controller's RAID features, instead exposing each disk to the OS
separately and using Linux's software RAID.

> What kind of hardware should I not buy to make sure this
> doesn't happen to me?

3ware's older cards. Apparently their new ones are a lot better, but I
haven't verified this personally.

Anything in RAID-5 without a BBU.

Anything at all without a BBU, preferably.

--
Craig Ringer