From: Paul Warren <pdw@ex-parrot.com>
To: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] High loads when writting to LVM
Date: Wed, 27 Oct 2004 16:27:40 +0100 [thread overview]
Message-ID: <20041027162740.J24976@sphinx.mythic-beasts.com> (raw)
In-Reply-To: <417FBB3D.6060002@ist.ucf.edu>; from jtracy@ist.ucf.edu on Wed, Oct 27, 2004 at 11:14:05AM -0400
On Wed, Oct 27, 2004 at 11:14:05AM -0400, Judd Tracy wrote:
> I have a system that I am testing out lvm on to get a feeling about
> stability and performance. Stability right now seems good, but I am a
> little worried about the performance currently I am writing out a large
> file ~1TB using dd if=/dev/zero of=test bs=1M and am noticing the load
> seams extreamly high "5.21, 5.26, 5.17". Most of the work is being done
> in dd but I also notice that kswapd0 is also working fairly heavily. Is
> this to be expected with LVM or do i have things setup wrong. Write
> performance seems to be around 100MB/s on an XFS filesystem.
This may be a result of how load average is calculated. What is the CPU
usage when doing these (see top)? On a machine with a large number of
processes accessing the disk, it is quite easy for a single, I/O
intensive application (such as your dd) to drive the load up.
The load average is telling you that you have 5 processes blocked
waiting for I/O. Without the dd, the time taken to service each is
reduced, and the average number blocked at any given time is therefore
lower.
On our combined shell/web/email server, an I/O intensive process will
result in a load of well over 10, yet responsiveness of the system
is not actually that bad, and cpu usage remains low.
Paul
prev parent reply other threads:[~2004-10-27 15:27 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-10-27 15:14 [linux-lvm] High loads when writting to LVM Judd Tracy
2004-10-27 15:27 ` Paul Warren [this message]
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