Re: P7 740 E6C EXP24S mode 1, disk upgrade options

"Steinmetz, Paul" <PSteinmetz@xxxxxxxxxx> wrote on Sun, 28 Dec
2014 22:52:55 GMT:

From what I read, you cannot mix SSD capacities and/or HDD in
a 5887, so a

2nd EXP24S would be required, if I keep existing 18 SSD.

You cannot mix HDD & SSD in the same 5887. You can mix
capacities all you want. However, this is not recommended.

It also appears that including disk units in an existing
parity set is no longer an option for Power8 foward and is not
recommended for newer generation SAS RAID adapters. "Including
disk units into an existing parity set with PCIe2, PCIe3, and
newer generations of SAS RAID adapters can result in a large
performance degradation"

Yes, this is the case. What it means is you must either a)
purchase the minimum quantity of additional devices to create
new parity sets or b) take the downtime to end parity protection
and start parity protection to protect the additional devices
you've purchased. This recommendation from the hardware
information center applied to 5913, EJ0L and P8 CEC DASD IOAs.

1) I could add 6 177 SSD, but not much gain in storage, only
a short term solution. 2) Replace existing 177 SSD with 775
SSD, very costly, but would be good for long term. 3) Add HDD
for cold data, using QAEZDISK from RTVDSKINF, I ran some
queries to analyze hot/cold data based on last use date, about
50/50 out of 2.8 TB. Adding a few HDD for 1.2 TB of cold data
hardly seems worth the hassle of a 2nd EXP24S, along with
running STRASPBAL *USAGE on a constant basis.

Maybe tagging most of your objects as UNIT(*SSD) and using
STRASPBAL *MP to move the "cold" stuff to HDD is a better option
for you since you'll have more GBs on HDD than SSD.

Another concern is the age of the 5887 EXP24S GEN2. Announced
4/12/11, will be 4 years old.

Do you recall how long IBM kept the 509x I/O towers around in
the marketplace? It was lots longer than 4 years. Looking at
the industry, things are moving to SAS generation 3 (12 Gbps)
disk I/O. How soon it will show up on Power Systems is anyone's
guess. IBM has not made any formal comments, statements of
direction or statements of intent in this arena.

Also, the 775 SSD GEN 3 were
announced 10/7/2013, 15 months old. Reviewing IBM announcement
history, I suspect both a new IO drawer and larger SSD drive
maybe around the corner, 1st qt 2015. If and when announced,
will it be supported on a P7 740 E6C?, maybe P8 only.

I can't really speak for the folks who make decisions regarding
what will be supported where. Looking at the past few
announcements made I will speculate support on non-P8 could be
limited to 'D' model P7s and the 795.