RE: Performance of large LF access path builds - SSD vs 10K spinny

Sue,

I also remember configuring our old Power5 to use "expert cache".
Does expert cache still apply on Power7.
How, where, do I check/do the expert cache config.

Paul

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Roberto José Etcheverry Romero
Sent: Wednesday, September 24, 2014 4:24 PM
To: Midrange Systems Technical Discussion
Subject: Re: Performance of large LF access path builds - SSD vs 10K spinny

Sue,
What you're describing would be akin to the Active/Passive controller configuration in the DS3/4/5xxx, and in those cases you need to have more LUNs to fully utilize both controllers. The same applies here, correct? at least 2 parity sets and the more the merrier?

Best Regards,

Roberto

On Wed, Sep 24, 2014 at 4:39 PM, Sue Baker <sue.baker@xxxxxxxxxx> wrote:

Evan Harris <auctionitis@xxxxxxxxx> wrote on Mon, 22 Sep 2014
18:49:31 GMT:

Could you please expand on that comment a little to explain why that
is ?

I'd just like to understand this a little better.

A single parity set will only utilize one of the paired adapters a the
path to/from storage devices to the system. In other words, you've
set things up so one active adapter and the second is acting as an
auxiliary write cache device. This is not how the adapter firmware
expects things to be and latency is introduced .... meaning longer
disk response times. True for both SSDs and HDDs, but more noticeable
with SSDs.


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