In order to understand the problem, you must understand at least at a high
level how IBM i does I/O. One of the biggest strengths of IBM i is its I/O
performance and that is achieved by building and I/O channel for each
storage device. Next it balances the I/O across all of the devices (or more
accurately across controllers, then devices) utilizing single level storage.
An ASP is an instance of single level storage (I'm purposely not being
complete here).
By putting the SSD devices in one ASP, and the spinning storage devices in
another ASP you will segregate the I/O allowing the faster SSD to not wait
on the slower technology since all the I/Os need to complete together before
the transaction is released by the OS back to the application.
So given that very short description of the underlying problem, why was
Roger's system set up with all the disk in one ASP, we can only guess, but
I'll point the finger at the partner that sold the system not following up
with the correct implementation plan. Doing that is advance storage
management and not many folks (as a percentage) in the IBM i community
really understand it well enough to implement it on their own. You need to
use the tooling to put the HOT files (high I/O) in the fast ASP (or pin them
to the SSD) and put the cold (low I/O) objects in the spinning technology.
In short, for the partner it was a quick way to increase the cost of the
system (and by definition their margin) and make the customer feel good
believing they did the right thing for the business.
Patrik: The OS should always be on the fast I/O technology. If you slow
down the OS, well, it follows that you slow the entire system down. Single
level storage and memory management both come into play here.
The correct implementation is not feasible now, so the best thing is to do
as Roger suggested in the first place, upgrade to all Flash or SSD on a P9.
Personally I would put up a V5030 with mixed storage technology and boot
from SAN (no drives in the P9) and allow EasyTier to figure it out for me.
--
Jim Oberholtzer
Agile Technology Architects
-----Original Message-----
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of Patrik
Schindler
Sent: Thursday, July 2, 2020 1:32 AM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: Mixing SSD & Spinny
Hello Roger,
Am 01.07.2020 um 23:51 schrieb Roger Harman <roger.harman@xxxxxxxxxxx>:
All in the same ASP
Maybe it's enough to just change that? System on spinning disks, data on
SSDs. I'd love to know what was the reason behind the system being set up
that way. I have some guesses but, well, it's guesses.
:wq! PoC
PGP-Key: DDD3 4ABF 6413 38DE -
https://www.pocnet.net/poc-key.asc
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