Message-Id: <200207031057.MAA03204@cave.bitwizard.nl>
Subject: Re: sync slowness. ext3 on VIA vt82c686b
In-Reply-To: <20020703094031.GA4462@lnuxlab.ath.cx> from khromy at "Jul 3, 2002
 05:40:31 am"
To: khromy <khromy@lnuxlab.ath.cx>
Date: Wed, 3 Jul 2002 12:57:45 +0200 (MEST)
CC: "Stephen C. Tweedie" <sct@redhat.com>, linux-kernel@vger.kernel.org,
       ext3-users@redhat.com
From: R.E.Wolff@BitWizard.nl (Rogier Wolff)
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khromy wrote:
> On Wed, Jul 03, 2002 at 10:22:44AM +0100, Stephen C. Tweedie wrote:
> > Ugh.  My first guess would be that you have one enormously fragmented
> > filesystem.  13MB in 2 minutes?  A modern disk should get that amount
> > of data to disk in one second, but massive fragmentation can simply
> > kill disk performance.
> > 
> > If /home is on the same disk, do you get the same problem trying to
> > write there?
> 
> Yeah, /home/ is on the same disk.  Your guess might be right because
> that's what I was trying to show.  When I copy the file, which is in
> /home/(hda2) to /tmp/(hda1) and I sync, it takes almost 2 minutes.  But 
> if I copy the same file, which is in /home/(hda2) to /usr/local/(hda3),
> sync returns immediately.  This disk isn't that old either.

Get your data off that disk Immediately!

If you write a large file, ext2 will do a good job not fragmenting the
file. You should be able to get about 20M per second on a sequential
writes, about 10M per second, if your filesystem is badly fragmented.

So, the drive is taking abnormally long to read/write blocks. That is
an indication that it's "going to die soon".

That said, maybe there is a whole lot of (random) reads going on 
on that disk? Are you swapping at the same time? Or maybe your
dayly "updatedb" is running?

Roger. 

-- 
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