Messages in this thread | | | Date | Wed, 22 Oct 2008 19:17:12 +0200 | From | Jens Axboe <> | Subject | Re: disk statistics issue in 2.6.27 |
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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 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 :)
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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