Messages in this thread | | | Date | Mon, 20 Oct 2008 19:12:48 +0200 | From | Jens Axboe <> | Subject | Re: disk statistics issue in 2.6.27 |
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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. > > To be sure it wasn't a bug in iostat I wrote a small perl script > to process /sys/block/sda/stats, and it shows the same problem. > > Note that the stats in /proc/diskstats and /sys/block/<dev>/stats > are the same. > > I've tried both the cfq and deadline I/O scheduler - no difference. > > $ perl mystat.pl > Device: r/s w/s rkB/s wkB/s > sda 141 53 2301120 1795200 > > Device: r/s w/s rkB/s wkB/s > sda 145 7 2366400 3394560 > > I compiled a 2.6.26.6 kernel with the exact same .config and it > doesn't show the problem. > > I've been staring at include/linux/genhd.h and block/genhd.c > for a while but I just don't see it. > > The mystat.pl perl script and my .config are below. > The machine is a dual xeon 2.2 Ghz, 32 bit, 4 GB mem, /dev/sda > is a 3-scsi-disk RAID5 array on an adaptec 2005S controller. > > Any idea what could be causing this ?
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?
Are the reported values in iostat any sort of multiple of the real throughtput, or is is just insanely large?
-- Jens Axboe
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