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Date:      Wed, 8 Nov 2000 16:58:30 -0800
From:      Alfred Perlstein <bright@wintelcom.net>
To:        Brian Behlendorf <brian@collab.net>
Cc:        stable@FreeBSD.ORG
Subject:   Re: disk I/O
Message-ID:  <20001108165829.F5112@fw.wintelcom.net>
In-Reply-To: <Pine.BSF.4.21.0011081625011.1844-100000@yez.hyperreal.org>; from brian@collab.net on Wed, Nov 08, 2000 at 04:35:13PM -0800
References:  <Pine.BSF.4.21.0011081625011.1844-100000@yez.hyperreal.org>

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* Brian Behlendorf <brian@collab.net> [001108 16:35] wrote:
> 
> RELENG_4, kernel last updated & built Aug 31st, so apologies if this
> touches a problem that was fixed since then.  I'd be happy to upgrade
> after 4.2-RELEASE goes out if people think there was a fix applied
> for this.
> 
> I'm having agonizingly slow disk I/O.  Granted, this is a heavily pounded
> machine (~2M web hits/day with ~50K being CGI or java, 500K mail
> deliveries using qmail, lots of CVS accesses) yet I get spikes in the load
> going up to 200 at times, during which the machine's largely frozen to
> shell access & other services are much slower.  It always comes back (go
> freebsd!) but it still feels like I/O is the culprit.  The CPU almost
> always has idle time available, yet during the day even doing an "ls" in a
> moderately sized dir is slow.  Here's iostat 5:

You have an IO problem that leads to a cascade failure, basically
everything starts piling up on the disks, because it's a multiuser
machine you're most likley having a lot of sparse access to the
drives so unlike your home machine you're probably doing a lot more
seeking which is killing performance.

I'd get a hardware raid system, they're a lifesaver for IO and
reliability.

best of luck,
-Alfred


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