[gbarth]

We have been doing some VIO disk I/O performance testing recently (disk is LUN from SAN) and getting the follwoing results

The VIO server partiton gets 350MBPS through put.
The AIX client partiton gets 220MBPS through put.

therefore access to the same LUN gets a 37% performance reduction from the AIX client. I assume there would be some overhead, but nothing on this scale.

Has anyone seen this before ?

Thanks.

[steevojb]

Hi

Interesting,

I will run the same test

What method are you using to write data ?
What is your SAN, what RAID configuration do you have ?

Regards

Steve

[gbarth]

hi steve,

the test is reading data with the dd command from /dev/rhdisk2

san is DS6800 (RAID5)

thanks in advance !!

[m_seger]

I have also run some quick tests with SAN Disks (DS4200) under VIO and
under LPAR.

VIO writes 512MB in 7sec. (dd if=/dev/zero) and LPAR needs
for the same tests 10sec. So I also have around 30% degradation!

This p570 is not doing anything else, it still smells like a new car ;-)

[dthacker]

Which one has higher CPU priority?

Dave

[m_seger]

@Dave

What do you mean with CPU Priority? Where can I check/change it?

Both Systems are "default" Installation with no parameters changed.

The VIO has an uncapped CPU, with max weight and there is nothing else
running on that system. So either an LPAR with direct attached FC Adapter
or a VIO with FC Adapter and an LPAR that uses VIO Resources was running.

I also get faster troughoutput with an old H50.

Cheers Mike

[sberube]

A few other things you wanna make sure of are...

1. that you have a min and max CPU for your VIO that are reasonable values (say 0.2 and 2 with an uncap weight of say 240... actually anything that's at least 30-50% higher than your other partitions so that if they are competing for processing resources, the VIO gets it. The rational behind this is if your VIO doesn't have any resources, none of your partitions can do anything).

2. that you have a number of virtual processor at least equal to your max cpu entitlement (if you have 1 vp and a max cpu of 2, you'll never be able to use more than 1 proc with your VIO).

3. try doing the test by sharing the lun directly to the partition (mkvdev -vdev hdiskX -vadapter vhostX -dev yadiyadiya) AND by sharing a LV to your partition (mkvdev -vdev SomeLV -vadapter vhostX -dev yadiyadiyaLV). If you are currently configured to share a drive that's under a VG and an LV in the VIO, your adding a bit of overhead you don't really need/want in this type of configuration.

Hopefully this can help!

Cheers.

[ross.mather]

A couple of thing sthat may help:

1. As per above from sberube, are there Logical volumes defined on the LUN at VIOS level or is the LUN directly connected through?

2. Are you using MPIO or SDD?

3. In the VIO Setup are you using multiple Fiber Channel Cards?

cheers
Ross