Re: New Large P9 SSD - 931 GB, 1.86 TB, 3.72 TB, and 7.45 TB - what are new rules for minimum number of arms

I do not believe IBM i will read and write through both channels simultaneously. My understanding is that one of each of the two paths is connected to one of the two RAID cards that control the drive. The RAID cards each 'own' some of the drives split up by RAID set. So if you have only one RAID set then only one of the two controllers will be doing any I/O at any one time and this would only change if that card failed. (Thus breaking your drives into even numbers of RAID sets behind each RAID card pair has performance benefits and is recommended.)

Even if it both paths could be used simultaneously that would be on the back side of the RAID card out in the SAS connection. Therefore IBM i itself wouldn't see those two channels it would only see the connection to the RAID card pair.

- Larry "DrFranken" Bolhuis

www.Frankeni.com
www.iDevCloud.com - Personal Development IBM i timeshare service.
www.iInTheCloud.com - Commercial IBM i Cloud Hosting.

On 8/9/2018 12:30 PM, Jim Oberholtzer wrote:

Agreed: Remember each DASD unit has two I/O channels so it can read/write
at the same time. Too few channels, and I don't care how fast the storage
is, it will not perform correctly. IBM i uses those channels for I/O. IBM
i does not give a rat's end what the storage really is since it's
virtualized anyway. (geesh I feel like I'm back in the bus/tag days with
the mainframe......)

Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects

On Thu, Aug 9, 2018 at 10:27 AM, DrFranken <midrange@xxxxxxxxxxxx> wrote:

Not fewer than 6 on any production system.

But, as usual, it matters what YOUR I/O load is six may still not be
sufficient.

- Larry "DrFranken" Bolhuis

www.Frankeni.com
www.iDevCloud.com - Personal Development IBM i timeshare service.
www.iInTheCloud.com - Commercial IBM i Cloud Hosting.

On 8/9/2018 11:22 AM, Steinmetz, Paul wrote:

With the new large P9 SSD announced, I have to ask, what is the
recommended minimum number of drives, obviously for performance only
reasons.
Our current production lpar is 7 tb, 13 - 775gb, Raid5, 2 Raid sets, 2
hot spares.

Theoretically, I could configure a new P9 with fewer SSD, various options.
The number of arms is the key question.
How many?

I was even considering combining all the LPARs DASD to one, which would
increase the number of arms, then letting it host the R&D and other LPARS.
Food for thought.
18-061 -IBM Power Systems enhances I/O with mainstream 2.5-inch SAS
SSDs

http://www-01.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/
ssi/rep_ca/1/897/ENUS118-061/index.html&lang=en&request_locale=en

Mainstream SSDs

New 931 GB, 1.86 TB, 3.72 TB, and 7.45 TB mainstream 2.5-inch SAS SSDs
are introduced for POWER9 and POWER8 technology-based servers using SAS
bays. These drives are supported in POWER9 and POWER8 system units (SFF-3)
and in expansion drawers such as the EXP24SX attached to POWER9 and POWER8
servers (SFF-2). With their large capacity and lower cost per gigabyte, the
drives can provide a very cost-effective and footprint-effective solution
for many mainstream configurations. Note these drives are designed for
workloads with modest write requirements, including as boot drives where
SSD performance is desired. These drives are rated at 1 DWPD, meaning you
can write 931 GB, 1.86 TB, 3.72 TB, or 7.45 TB to the SSD every day for
five years, nearly 1.7 PB for the 931 GB SSD.

Thank You
_____
Paul Steinmetz
IBM i Systems Administrator

Pencor Services, Inc.
462 Delaware Ave
Palmerton Pa 18071

610-826-9117 work
610-826-9188 fax
610-349-0913 cell
610-377-6012 home

psteinmetz@xxxxxxxxxx
http://www.pencor.com/

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