linux-kernel - Re: disk statistics issue in 2.6.27

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Date:	Wed, 22 Oct 2008 16:37:52 +0200
From:	Miquel van Smoorenburg <mikevs@...all.net>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org
Subject: Re: disk statistics issue in 2.6.27

On Mon, 2008-10-20 at 19:12 +0200, Jens Axboe wrote:
> On Sun, Oct 19 2008, Miquel van Smoorenburg wrote:
> > I just upgraded one of our servers in the nntp cluster to 2.6.27.1 -
> > most of the others are running 2.6.26.something.
> > 
> > I noticed that the "iostat -k -x 2" output does't make any sense.
> > The number of reads/sec and number of writes/sec are about what I
> > would expect, and so are the other fields, but rkB/sec and wkB/sec
> > are  completely off-scale: gigabytes read/written per second.
>
> Weird, I cannot reproduce this at all, iostat works fine for me in .26,
> .27 and current -git as well. So it's just a plain SCSI drive from
> linux, no software raid or dm?

It's a 3-disk hardware RAID5 array, Adaptec 2005S, dpt_i2o driver.

> Are the reported values in iostat any sort of multiple of the real
> throughtput, or is is just insanely large?

It looks like it's a multiple, but it appears to vary between 128 and
512, and is different for reads and writes, so I do not know what to
make of it.

I tried to reproduce it on different systems - on another box with a
2010S controller I'm seeing the same thing. But on a different box with
SATA drives I cannot reproduce the problem.

Thanks for looking at this. I guess I'll have to start putting debug
statements in block/gendisk.c to find out what's wrong. I might not have
time for it until after next week though, but I won't give up :)

Mike.

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