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Re: inferior SCSI performance

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: adler(at)pobox(dot)com
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: inferior SCSI performance
Date: 2003-09-17 19:08:33
Message-ID: 4693.1063825713@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Michael Adler <adler(at)pobox(dot)com> writes:
> I have been experimenting with a new Seagate Cheetah 10k-RPM SCSI to
> compare with a cheaper Seagate Barracuda 7200-RPM IDE (each in a
> single-drive configuration). The Cheetah definately dominates the generic
> IO tests such as bonnie++, but fares poorly with pgbench (and other
> postgresql operations).

It's fairly common for ATA drives to be configured to lie about write
completion (ie, claim write-complete as soon as data is accepted into
their onboard RAM buffer), whereas SCSI drives usually report write
complete only when the data is actually down to disk.  The performance
differential may thus be coming at the expense of reliability.  If you
run Postgres with fsync off, does the differential go away?

			regards, tom lane

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