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Latency on Clariion & SVC but none on Symmetrix

Gaël LEPETIT
Occasional Advisor

Latency on Clariion & SVC but none on Symmetrix

Hi all,

There's a strange behaviour on our elderly 11.00 servers

A 2 & 6 seconds latencies occurs when opening a Clariion or IBM SVC LUNz.
But, when accessing Symmetix LUN, the result appears instantly :

example :
Average results of the commmand : time dd if=/dev/rdsk/c80t0d0 of=/dev/null bs=1024k count=10
Symmetrix : 0.2s
Clariion CX3-80: 3s
IBM SVC : 6s

Same results with a simple "diskinfo". The big lag occurs.

But with a higher volume of data, we see a normal throughput (if substract the lag) :
Average results : bs=1024k count=300
Symmetrix : 9s
Clariion : 6s
IBM SVC : 9.5s

Average results : bs=1024k count=1000
Symmetrix : 41s
Clariion : 14,4s
IBM SVC : 17,7s

The server is fully patched and the FC driver is the newest-one.

Does somebody have the idea ?
http://quelquesbrassesdanslesysteme.blogspot.com/
4 REPLIES
Mel Burslan
Honored Contributor

Re: Latency on Clariion & SVC but none on Symmetrix

Even though this much latency can not solely be attributed to it but considering Symmetrix is a shirt or two above Clariion series (I am not sure about the IBM as I never touched it) some sort of performance difference is expected between the two EMC product series.

Also the load on the devices as well as their front-end cache memory sizes can cause wildly varying performance stats that I know of. So checking the cache sizes and load amount on each of these back end frames, may bring a better explanation to the situation.
________________________________
UNIX because I majored in cryptology...
Rita C Workman
Honored Contributor

Re: Latency on Clariion & SVC but none on Symmetrix

I don't work with IBM storage, but I know EMC storage and yes, just as Mell says, the Symmetrix will always perform better than the Clariion.
Your Clariion is even an older version, so add that to the results as well.

Your apples to oranges. Not the same.

Rgrds,
Rita

Gaël LEPETIT
Occasional Advisor

Re: Latency on Clariion & SVC but none on Symmetrix

IBM SVC is just a front-end for Clariion or V-Max arrays.
The bandwidth is limited by the 1gbs hba cards not by the array itself.

The patch who saved my perfs is PHKL_34186.

And here's the root cause :

open(2) command sequence takes a long
time for SPC-2 compliant devices.

# time dd if=/dev/rdsk/c80t0d0 of=/dev/null bs=1024k count=10

Before the patch :
IBM SVC : 6s

After :
IBM SVC : 0.2s
http://quelquesbrassesdanslesysteme.blogspot.com/
Gaël LEPETIT
Occasional Advisor

Re: Latency on Clariion & SVC but none on Symmetrix

Closing thread
http://quelquesbrassesdanslesysteme.blogspot.com/