problems getting ioband to work properly
Hi,
Thanks for being interested in dm-ioband.
> I'd like to try I/O shaping using ioband, but it doesn't seem to be working properly for some reason.
> I have one disc partition used as LVM PV, VG on top of it. I created two 1GB LVs for tests: iob1, iob2
>
> Then I setup ioband using following commands:
>
> echo 0 2097152 ioband /dev/mapper/vg-iob1 iob 0 0 none weight 0 :40 | dmsetup create ioband-iob1
> echo 0 2097152 ioband /dev/mapper/vg-iob2 iob 0 0 none weight 0 :10 | dmsetup create ioband-iob2
>
> When I measure throughput using hdparm --direct -t on one of the ioband devices, i get ~61MBps.
>
> If I measure it on both devices concurrently in loop, throughput settles on ~30MBps on every device, so it seems that it's divided equally.
>
> What am I doing wrong?
Dm-ioband is designed not to limit the I/O bandwidths of disks unless
the I/O load is heavy so that you can use the full performance of
the disks, which can handle multiple I/O requests at the same time.
Dm-ioband starts controlling I/O bandwidth when the number of I/O
request exceeds a certain threshold, which can be changed with
dmsetup command.
# sudo dmsetup message ioband-iob1 0 io_throttle 2
Please see also the manual at:
http://people.valinux.co.jp/~ryov/dm-ioband/manual/cmdref.html
If you do the following, you will see how the bandwidth control is working.
1. run a total of eight dd programs for reading.
#!/bin/bash
for ((i = 0; i < 4; i++)); do
dd if=/dev/mapper/ioband-iob1 of=/dev/null ibs=4k iflag=direct &
dd if=/dev/mapper/ioband-iob2 of=/dev/null ibs=4k iflag=direct &
done
2. watch the iostat report at intervals of 5 seconds.
# iostat -p dm-2 -p dm-3 5
...
avg-cpu: %user %nice %system %iowait %steal %idle
1.24 0.00 23.40 29.28 0.00 46.08
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
dm-2 4647.33 37178.60 0.00 180688 0
dm-3 1348.56 10788.48 0.00 52432 0
avg-cpu: %user %nice %system %iowait %steal %idle
0.73 0.00 23.11 26.11 0.00 50.05
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
dm-2 5092.75 40742.03 0.00 196784 0
dm-3 1019.25 8154.04 0.00 39384 0
...
Thanks,
Ryo Tsuruta
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