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Re: [Xen-users] High iowait every day at the same time.

To: Simon Hobson <linux@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] High iowait every day at the same time.
From: Michael Borokhovich <michaelbor@xxxxxxxxx>
Date: Tue, 5 Oct 2010 22:45:19 +0200
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
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Simon, thank you very much.

Since all my VMs are running Debian, there was the cron.daily schedule at 8:25 in /etc/crontab file. The problematic process was 'updatedb' which was initiated by the 'find' script in the cron.daily directory.

I will comment this line in /etc/crontab and it hopefully will solve the problem.

Thanks again,

On Fri, Oct 1, 2010 at 09:18, Simon Hobson <linux@xxxxxxxxxxxxxxxx> wrote:
Michael Borokhovich wrote:

I have a strange and the same problem on two servers. I'm running Xen on two different servers ( Debian 4.0 and 2.6.18-xen Debian 4.0). About 120 guest domains.
Every day exactly at 08:25 AM, high iowait ~99% load starts and lasts for about 50 minutes.

When guests domains are shut down, the problem is not appearing. There is no tasks in crontab on Domain0 and on guest domains.

By default, Debian runs a bunch of tasks at 6:25, have a look in /etc/cron.* and /etc/crontab. I see you are in a +2 timezone, so that would make 6:25 into 8:25 by my reckoning.

If you have a lot of guests all firing up at the same time, then that could well saturate your I/O and make it all slow down.

Simon Hobson

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