Re: SSD + RAID

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Matthew Wakeling <matthew(at)flymine(dot)org>
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>, Laszlo Nagy <gandalf(at)shopzeus(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: SSD + RAID
Date: 2010-02-20 18:28:55
Message-ID: 201002201828.o1KIStQ12830@momjian.us
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Matthew Wakeling wrote:
> On Fri, 13 Nov 2009, Greg Smith wrote:
> > In order for a drive to work reliably for database use such as for
> > PostgreSQL, it cannot have a volatile write cache. You either need a write
> > cache with a battery backup (and a UPS doesn't count), or to turn the cache
> > off. The SSD performance figures you've been looking at are with the drive's
> > write cache turned on, which means they're completely fictitious and
> > exaggerated upwards for your purposes. In the real world, that will result
> > in database corruption after a crash one day.
>
> Seagate are claiming to be on the ball with this one.
>
> http://www.theregister.co.uk/2009/12/08/seagate_pulsar_ssd/

I have updated our documentation to mention that even SSD drives often
have volatile write-back caches. Patch attached and applied.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
PG East: http://www.enterprisedb.com/community/nav-pg-east-2010.do
+ If your life is a hard drive, Christ can be your backup. +

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