AIX lpar bad disk I/O performance - 4k per IO limitation ?
Hi Guys,
I have fresh new installed VIO 2.2.3.70 on a p710, 3 physical SAS disks, rootvg on hdisk0
and 3 VIO clients through vscsi, AIX7.1tl4 AIX6.1tl9 RHEL6.5ppc, each lpar has its rootvg installed on a LV on datavg (hdisk2) mapped to vhost0,1,2
There is no vg on hdisk1, I use it for my investigation.
hdisk1 is mapped to all 3 lpar AIX7.1tl4 AIX6.1tl9 RHEL6.5ppc through the same vhost0,1,2
from VIO server, "dd if=/dev/hdisk1 of=/dev/null bs=1M" running in parallel "iostat -DlT 1", gives me a throughput of 93.2MB/s (AS EXPECTED)
from lpar1 AIX7.1tl4 , "dd if=/dev/hdisk1 of=/dev/null bs=1M" running in parallel "iostat -DlT 1" on the VIOserver, gives me a throughput of 10MB/s (TOO LOW !)
from lpar2 AIX6.1tl9 , "dd if=/dev/hdisk1 of=/dev/null bs=1M" running in parallel "iostat -DlT 1" on the VIOserver, gives me a throughput of 10MB/s (TOO LOW !)
from lpar3 RHEL6.5ppc, "dd if=/dev/sdb of=/dev/null bs=1M" running in parallel "iostat -DlT 1" on the VIOserver, gives me a throughput of 113MB/s (AS EXPECTED)
ofcourse the dd commands are run separetely each time. there is clearly bad performance on the AIX lpars, I tried to modify few parameters such queue_depth or max_transfer with the same result.
See below the iostat outputs on the VIO for each test.
If I compare the bps and tps value :
on the VIO where the disk is local, 22761 I/O requests give 93MB/s (about 4k per I/O as per my calculation)
on the VIO clients which run AIX, 2500 I/O requests give 10MB/s (about 4k per I/O as per my calculation)
on the VIO client which runs RHEL, 1730 I/O requests give 113MB/s (about 66k per I/O as per my calculation)
it seems the io size is limited to 4k on AIX, and that could be the thing to modify ...
Do you have any idea which parameter I could modify to get acceptable performance on aix lpar ?
Please note that there is no filesystem nor LVM in the picture, I access directly the hdisk through vscsi, that's it. so the Filesystem tuning nor LVM tuning is not relevant in my case.
---------- Post updated at 10:43 PM ---------- Previous update was at 09:34 PM ----------
I think I got my answer, I was simply "dd if=/dev/hdiskX ..." and I should have done "dd if=/dev/rhdiskX ..."
using the raw device instead of the block device increased the iostat result significantly !
Although on linux I was using the block device, I didn't get such difference with the raw device.
To dd the raw device on linux I have done :
Code:
[root@lpar3 ~]# raw /dev/raw/raw1 /dev/sdb
/dev/raw/raw1: bound to major 8, minor 16
[root@lpar3 ~]# dd if=/dev/raw/raw1 of=/dev/null bs=1M
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