On Tue, Aug 29, 2006 at 11:39:57AM +0900, Tejun Heo wrote:
> Derek Taubert wrote:
> ># dd if=/dev/zero of=/dev/sda1 count=4M
> ><ctrl-c, then wait 30 seconds>
> >264205+0 records in
> >264204+0 records out
> >135272448 bytes (135 MB) copied, 111.373 seconds, 1.2 MB/s
> >
> >From iostat -k 10:
> >Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
> >sda 2428.64 2422.46 667.66 24273 6690
> >sda 36.84 23.72 1667.87 237 16662
> >sda 2440.60 2434.90 616.00 24349 6160
> >The read rate is curious (should be 0)...
> >
> >Top shows 1% user, 3% system, 93% wait.
>
> It seems some kind of read IO is in progress. Can you repeat the test
> on an unused/idle (iostat -k 10 shows all zeros...) drive? The above
> result actually looks good if you consider both read and write sides.
I think that 3MBytes/sec total for a drive that can read at 50MBytes/sec
on the same system is quite bad, especially since we're talking about
a linear write test.
> The result doesn't seem to indicate any problem in libata or any storage
> related kernel subsystem. I would track down the reader first.
This drive has only been partitioned; there is no filesystem on it. So,
it certainly isn't mounted anywhere. There honestly isn't _anything_
other than the dd going on to sda1, and that's the only partition on
sda.
> >2) hdparm -C for all 4 drives always shows "drive state is: standby"
> > even when I'm certain that the drives are active.
>
> hdparm -C says the same thing for my drive. I think it's safe to
> ignore. Hmmm... it needs to be tracked down. Maybe some problem in
> HDIO ioctl implementation in libata.
It's a "nice to have" for using smartd. ie: don't spin the drives up to
poll the failure attributes, but they should be checked if the drive's
already active.
> >I'd really like some assistance debugging the write performance issue.
> >The "hdparm -C" issue would be gravy...
>
> Please track down the reader.
Before running dd (fuser -v /dev/sda1 shows nothing):
avg-cpu: %user %nice %sys %iowait %idle
0.50 0.00 0.20 0.00 99.30
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
fd0 0.00 0.00 0.00 0 0
hda 0.00 0.00 0.00 0 0
md0 0.00 0.00 0.00 0 0
md1 0.00 0.00 0.00 0 0
sda 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
sdc 0.00 0.00 0.00 0 0
sdd 0.00 0.00 0.00 0 0
After starting dd:
# fuser -v /dev/sda1
USER PID ACCESS COMMAND
/dev/sda1 root 21753 f.... dd
avg-cpu: %user %nice %sys %iowait %idle
0.90 0.00 11.01 88.09 0.00
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
fd0 0.00 0.00 0.00 0 0
hda 0.10 0.00 0.40 0 4
md0 0.00 0.00 0.00 0 0
md1 0.00 0.00 0.00 0 0
sda 1306.61 1295.60 1310.11 12943 13088
sdb 0.00 0.00 0.00 0 0
sdc 0.00 0.00 0.00 0 0
sdd 0.00 0.00 0.00 0 0
After stopping dd (fuser -v /dev/sda1 again shows nothing):
avg-cpu: %user %nice %sys %iowait %idle
0.80 0.00 0.30 0.00 98.90
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
fd0 0.00 0.00 0.00 0 0
hda 1.00 0.00 5.21 0 52
md0 0.00 0.00 0.00 0 0
md1 0.00 0.00 0.00 0 0
sda 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
sdc 0.00 0.00 0.00 0 0
sdd 0.00 0.00 0.00 0 0
I'm honestly not sure what else to check...
Thanks for your response,
Derek
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