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Re: Two hard drives --- what to do with them?

From: Bruno Wolff III <bruno(at)wolff(dot)to>
To: Peter Kovacs <maxottovonstirlitz(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Carlos Moreno <moreno_pg(at)mochima(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Two hard drives --- what to do with them?
Date: 2007-03-01 03:28:46
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Sun, Feb 25, 2007 at 23:11:01 +0100,
  Peter Kovacs <maxottovonstirlitz(at)gmail(dot)com> wrote:
> A related question:
> Is it sufficient to disable write cache only on the disk where pg_xlog
> is located? Or should write cache be disabled on both disks?

With recent linux kernels you may also have the option to use write
barriers instead of disabling caching. You need to make sure all of
your stacked block devices will handle it and most versions of software
raid (other than 1) won't. This won't be a lot faster, since at sync
points the OS needs to order a cache flush, but it does give the disks a chance
to reorder some commands in between flushes.

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