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

From: "Peter Kovacs" <maxottovonstirlitz(at)gmail(dot)com>
To: "Jeff Davis" <pgsql(at)j-davis(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: 2007-02-27 00:11:24
Message-ID: b6e8f2e80702261611j598b1771g3dbcfc9bb1f9cdf2@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On 2/26/07, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> 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.

Sorry for for not being familar with storage techonologies... Does
"battery" here mean battery in the common sense of the word - some
kind of independent power supply? Shouldn't the disk itself be backed
by a battery? As should the entire storage subsystem?

Thanks
Peter

>
> Regards,
>         Jeff Davis
>
>

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