 | | | I/O Utilization Statistic Strangeness in U5 | I/O Utilization Statistic Strangeness in U5 2005-06-13 - By Dag Wieers
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On Mon, 13 Jun 2005, Tom Sightler wrote:
> Over the weekend we upgraded several of our RHEL3 systems to U5 and
> since then we have noticed that our network monitoring started alerting
> us to high IO utilization values on multiple servers. Upon looking into
> this problem we've found that running 'iostat -x 1' does show 100%
> utilization even though nothing is really going on on the disk. It
> would appear that this might be a bug in iostat, or that something
> changes in /proc/partitions that iostat was using because older versions
> of iostat report even stranger numbers.
>
> Also, if we reboot a system it initially reports normal, but continues
> to grow as IO occurs. This would imply that iostat might be reading the
> wrong information from /proc/partitions.
>
> Anyone else seeing this or is it some uniqueness on our systems?
>
> Running a quick 'iostat -x 1' and see if any of your drives show 100%
> utilization would be an easy way to show it.
I can confirm the behaviour of iostat, but there has been no change in
the /proc/partitions format, I verified this with older copies.
My suspicion goes out to the values in /proc/partitions and /proc/stat.
iostat is using both files to make up the utilisation percentage. You can
see both with:
watch -n1 -d -- head -15 /proc/partitions /proc/stat
The 2 last values in /proc/partitions seems to be resp. increasing and
decreasing at a constant rate while the disks are not being used. So
there's a bug in the kernel updating these counters.
Tom, can you put your info together with this in a bugzilla report (first
check if there's not already one). That would be appreciated :)
Kind regards,
-- dag wieers, dag@(protected), http://dag.wieers.com/ --
[all I want is a warm bed and a kind word and unlimited power]
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