[ILUG] Extremely slow/CPU intensive SATA IO on 2 CPU HT server.

[Robert Sweetnam]

> On 12 Mar 2006, at 19:02, David Wilson wrote:
>
> > Hi folks,
> >
> > We have a dual 2.8ghz Xeon server with 2gb RAM running vanilla
> > 2.6.15.1
> > which is seeing some really odd IO behaviour. I've always been aware
> > that the machine felt slightly more sluggish than it should have, but
> > upon running an extremely simple UPDATE on 80,000 or so rows in
> > PostgreSQL last night, the machine crapped itself and jumped to a load
> > of 8.0.
> >
>

What distribution and what exact CPU?

Have had similar problems running CentOS with kernel 2.6.9-11 on a
Dual Core Xeon with EMT64. Problem seemed to be resolved when I
changed the OS to Ubuntu 5.10 x64.Its a  test machine so I had the
luxury of being able to experiment but might be worth checking out all
the same.

Specifically what led me to change was I was originally running SuSE
9.1 32bit and had problems with exceptionally low disk benchmarks
using  hdparm -tT . Hardware is SCSI but AFAIK SATA uses a SCSI
wrapper.. Cant remember the exact specifics of the original benchmark
but now it reports the following:

Timing cached reads:   3204 MB in  2.00 seconds = 1599.84 MB/sec
Timing buffered disk reads:  382 MB in  3.08 seconds = 124.04 MB/sec

For the record Ubuntu kernel is 2.6.12-10-amd64-generic

Might be worth exploring or might not.. just my 2c..

Cheers
Robert