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SubjectRe: disk statistics issue in 2.6.27
On Wed, Oct 22 2008, Miquel van Smoorenburg wrote:
> 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 -
> > > 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 :)

It's all really weird, especially if you see it on drivers both using
the SCSI layer. And it's a multiple of the transfer size, then it can't
be something like requeues skewing the count. But do look into it, I'll
do some testing on various drivers tomorrow as well.

Jens Axboe

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