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RE: New Power8 Disk Perf Issues



fixed

Sue,

<I will agree for POWER7 and earlier systems. I will disagree for the POWER8 S814 and S824 models with high function backplane. The on-board disk IOAs are better than the feature
ESA3 and 5913 adapters used by many on POWER7 for write
intensive and write response time sensitive workloads.>

When you state high function backplane, you're referring to <Third is high function backplace with 7.6GB of write cache and maximum drive bays.> correct?

So, if using CEC's DASD, you should almost always consider option 3 from a performance point of view.

Also, are you stating the option 3 is equal or outperforms a 5913.
So a fully loaded CEC with 8 775gb SSD (5.4 tb useable with Raid 5) with option 3, high function backplane would be about the best performance for an i5/0S LPAR.

Or, what would be better?

Paul

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Sue Baker
Sent: Tuesday, August 26, 2014 1:50 PM
To: midrange-l@xxxxxxxxxxxx
Subject: RE: New Power8 Disk Perf Issues

"Steinmetz, Paul" <PSteinmetz@xxxxxxxxxx> wrote on Tue, 26 Aug
2014 15:13:15 GMT:

Why would you pick a backplane option with 0 write cache.

If the workload is not sensitive to write response time, write cache is not a factor. If you utilize SSDs, even with a 2ms average write response time, the lack of write cache may not be a factor for the workload.

History has proven that the CEC with 0 write cache will be a
performance issue.

The adapters in the POWER7 and earlier CECs had limited IOPS and MB/s throughput capabilities. In many cases, these limitations and not the lack of write cache was the real culprit for poor performance.

History also has shown that the CEC should be avoided for a production
lpar.


I will agree for POWER7 and earlier systems. I will disagree for the POWER8 S814 and S824 models with high function backplane. The on-board disk IOAs are better than the feature
ESA3 and 5913 adapters used by many on POWER7 for write
intensive and write response time sensitive workloads.


--
Sue
IBM Americas Advanced Technical Sales Support (ATS) Power Systems Rochester, MN
--
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