[CentOS] Extremely slow disk transfers with SATA disks

Peter Kjellström cap at nsc.liu.se
Fri Mar 24 11:13:25 UTC 2006


On Friday 24 March 2006 08:31, vanja at pobox.com wrote:
> On Thu, Mar 23, 2006 at 04:54:44PM +0100, Peter Kjellström wrote:
> > On Thursday 23 March 2006 15:37, Vanja Hrustic wrote:
> > > ...
> > Have you tried to figure out if it's reading or writing or both that
> > suck? try this:
> >
> > time dd if=/dev/zero of=testfile bs=1M count=1000
> >
> > time dd if=testfile of=/dev/null bs=1M
> >
> > If you have 1 gig ram or more adjust count...
>
> As usual, I get to test more things only after I make a post to the mailing
> list :)

fwiw, it was a very good bugreport making progress easy.

> What I found out is that 1 disk is creating problems (out of those 2), and
> only when reading.
>
> So, that 200GB Maxtor has no problems writing (300MB file gets written in
> few seconds, when it's read from another 80GB SATA disk), but when I read
> something from that disk - I get 2MB/sec. I have no trouble reading from
> 80GB SATA disk, so I guess it will be cable/hardware related.
>
> Also, I said it works ok in Windows, but Windows partition is located on
> 80GB drive. 200GB drive only holds Linux partitions.
>
> I have no idea why hdparm reports 50MB/sec rates on 200GB disk, but I'll
> just assume that hdparm doesn't use "real life" way of testing speed :)

It just reads, and only at the beginning of the device.

/Peter

>
> Thanks for feedback. I will post again when/if I fix this, and figure out
> if it was indeed a hardware problem.
>
> Take care.
>
> Vanja

-- 
------------------------------------------------------------
  Peter Kjellström               |
  National Supercomputer Centre  |
  Sweden                         | http://www.nsc.liu.se
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