sar -d avg

[Deepak Seth_1]

Hello Everybody,
What we have :

EMC symm 1569
3 fiber cards - that means 3 alternate links
EMC powerpath.
lv created using :
lvcreate -L 4320 -i 3 -I 16 /dev/...

Attached is the output of sar -d 1 10 . The avque lenght showing a value of more than 65,000 . Also the avg wait is more than avgserv.


Is a too small striping an issue. I have already rebooted my machine.

EMC & HP have no idea except re-creating a lv's with a different stripe sizes and see the results.
Pls. suggest .

thanx in advance.

[Paula J Frazer-Campbell]

Hi

How are your disks configured?

Looks like 9 in the VG ?

How are they stripped ?

The %busy is not high - are you seeing any problems.

What is the data and waht do you do with it i.e. read to write percentage?

Are the processors busy and so slowing down r/w to disk?

What does sar -b %rcache show? are you getting 100 hit rate from it?

Paula

[Alan Riggs]

Can you clarify for me, please?

You have 3 connections to the SYM. Check.
You have EMC Powerpath. Check
Your lvcreate lists a stripe depth of 3. Are these 3 separate hypers being published to you by the SYM? Or is this the 3 links shown by powerpath to the same hyper?

If the latter, that is your problem. You would be striping to the same physical volume. You only want to add one Powerpath device into your VG/LV. You don't even need to add the shadow link; Powerpath will take care of both failover and loadbalancing for you.

If it is just a coincidence, then I am mystified. I think you will find better performance by setting the stripe size to 32, which matches the size of EMC buffer entries, I believe, but I don't think that would be enough difference to explain what you are seeing.

[Deepak Seth_1]

On EMC side - 73 gig curved to 8.7 gig LUN.

On Host Side - A vg contains 3 PV of 8.7 gig each . Each lvol is stiped over to 3 PV's using stripe size of 16K .

There is no performance problem repoted by users and memory and cpu utilisation remain fine. The sar -b shows a %readchace of around 95+ always .

Attached is the pvdisplay output.