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Old 07-01-2008, 12:11 PM
Nikola Ciprich
 
Default problems getting ioband to work properly

Hello all,
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?

thanks a lot in advance

nik

PS: I'm using 2.6.26-rc8+ioband-1.1.0 patch

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Old 07-03-2008, 12:53 PM
Ryo Tsuruta
 
Default 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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