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

From: Jeff Davis <pgsql(at)j-davis(dot)com>
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: 2007-02-26 21:51:06
Message-ID: 1172526666.10824.315.camel@dogma.v10.wvs (view raw or flat)
Thread:
Lists: pgsql-performance
On Sun, 2007-02-25 at 23:11 +0100, Peter Kovacs 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?
> 

When PostgreSQL does a checkpoint, it thinks the data pages before the
checkpoint have successfully made it to disk. 

If the write cache holds those data pages, and then loses them, there's
no way for PostgreSQL to recover. So use a battery backed cache or turn
off the write cache.

Regards,
	Jeff Davis


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