Re: Best OS & Configuration for Dual Xeon w/4GB &

-----Original Message-----
From: "Luke Lonergan"<llonergan(at)greenplum(dot)com>
Sent: 19/03/06 16:26:58
To: "Kenji Morishige"<kenjim(at)juniper(dot)net>, "Claus Guttesen"<kometen(at)gmail(dot)com>
Cc: "pgsql-performance(at)postgresql(dot)org"<pgsql-performance(at)postgresql(dot)org>
Subject: Re: [PERFORM] Best OS & Configuration for Dual Xeon w/4GB &

> I notice that no one asked you about your disk bandwidth - the Adaptec 2200S
>is a "known bad" controller -

Agreed - We have a couple at work which got relagated to use in 'toy' boxes when we realised how bad they were, long before they ever saw any production use.

Regards, Dave

-----Unmodified Original Message-----
Kenji,

On 3/17/06 4:08 PM, "Kenji Morishige" <kenjim(at)juniper(dot)net> wrote:

> Thanks guys, I'm studying each of your responses and am going to start to
> experiement.

I notice that no one asked you about your disk bandwidth - the Adaptec 2200S
is a "known bad" controller - the bandwidth to/from in RAID5 is about 1/2 to
1/3 of a single disk drive, which is far too slow for a 10GB database, and
IMO should disqualify a RAID adapter from being used at all.

Without fixing this, I'd suggest that all of the other tuning described here
will have little value, provided your working set is larger than your RAM.

You should test the I/O bandwidth using these simple tests:
time bash -c "dd if=/dev/zero of=bigfile bs=8k count=1000000 && sync"

then:
time dd if=bigfile of=/dev/null bs=8k

You should get on the order of 150MB/s on four disk drives in RAID5.

And before people jump in about "random I/O", etc, the sequential scan test
will show whether the controller is just plain bad very quickly. If it
can't do sequential fast, it won't do seeks fast either.

- Luke

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