If VIO Server is hosting the disk (usually iSCSI) then it generates lots of
I/O. If it's using NPIV to host SAN disk then it generates less I/O, so the
answer is "it depends".
In Agile's case the completely hosted iSCSI partitions have good to
excellent performance. The partitions with NPIV and a V3700 scream fast.
There is a marked difference even with my very light workloads. My disk
controller has cache. (P7 4way with 64GB memory, six partitions, one
processor)
I have one customer that does not have cache and I/O performance is abysmal.
--
Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects
-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of
Mitchell, Dana
Sent: Tuesday, August 26, 2014 10:47 AM
To: Midrange Systems Technical Discussion
Subject: RE: New Power8 Disk Perf Issues
I would guess that 0 write cache is intended for all/mostly SSD
configuration. Or perhaps just VIOS disks in the CEC, VIOS probably
doesn't generate much write activity to it's disks once it's up and running.
Dana
-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of
Steinmetz, Paul
Sent: Tuesday, August 26, 2014 10:13 AM
To: 'Midrange Systems Technical Discussion'
Subject: RE: New Power8 Disk Perf Issues
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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