Re: New Power8 Disk Perf Issues

Paul

I'd asked the same question when I first saw this, and presented it to my boss.

Turns out that when all data is on a SAN, that the write cache is less important - here is a note I took from a presentation by Sue Baker to the CAAC -

1.Connecting to existing SAN -- will use fibre channel

Write caching is done on fibre adapter, so might not need it on CEC


If you use the $4K controller, you do have more slots for disk - suggesting local storage. And for that you definitely want write cache.

HTH
Vern

On 8/26/2014 10:13 AM, Steinmetz, Paul wrote:

Why would you pick a backplane option with 0 write cache.
History has proven that the CEC with 0 write cache will be a performance issue.
History also has shown that the CEC should be avoided for a production lpar.

Paul

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Jim Oberholtzer
Sent: Tuesday, August 26, 2014 11:10 AM
To: 'Midrange Systems Technical Discussion'
Subject: RE: New Power8 Disk Perf Issues

Thanks for the clarification Sue. The literature is not clear on those point.

--
Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects


-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Sue Baker
Sent: Tuesday, August 26, 2014 9:44 AM
To: midrange-l@xxxxxxxxxxxx
Subject: RE: New Power8 Disk Perf Issues

"Jim Oberholtzer" <midrangel@xxxxxxxxxxxxxxxxx> wrote on Mon, 25 Aug 2014
18:24:28 GMT:

We know that P8 will use internal storage, except, as I understand it,
if you have the back plane split so you can run dual VIO Servers.

No, the split backplane is supported by IBM i so you do not have to run dual VIO servers. This means you could have VIOS for NPIV using 1/2 the disk bays. Then sitting right beside an IBM i LPAR using the other 1/2 of the disk bays.

Then you must use external storage.

Even if you do dual VIOS, there are card slots for disk IOAs which can be dedicated to an IBM i LPAR. I'm not sure why you say with split backplane storage must be external SAN. Unless you really meant storage will be external to the CEC.

So
it's about half right. Even then I think you might get away with
internal storage but it would be A) slow and B) very limiting so
certainly not recommended.

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