Re: EJ1D/EJ1M Write Cache (Was Is this S914 config a good replacement for my S814 ?

date: Sun, 1 Apr 2018 11:25:03 -0400
from: DrFranken <midrange@xxxxxxxxxxxx>
subject: Re: EJ1D/EJ1M Write Cache (Was Is this S914 config a good
replacement for my S814 ?)

See in line!

On 4/1/2018 2:23 AM, Gad Miron wrote:

Jim, Larry, Paul - THANKS again



This EJ1D/EJ1M issue is out of my depth :-(


The quote specifies a " 2 x 1.8GB native 7.2GB compressed" but no card
No. - I'll ask for details.

Normal because there are no choices it's either in there or not in
there. :-)

I guess this is indeed the on-board/embedded controller. (and if I
understood correctly it better be a EJ1D rather than EJ1M)

Although the cards are the same the EJ1M would have a different DASD
Backplane and thus only support 12 drives.

I remember asking if this is a PCIe3 card and was answered it's not, it

is

a PCIe2 one

I'm going to disagree. One of the engineers told me this rule that while
not set intentionally worked out very well. It is a hard rule, not a
'guideline' :-)

PCIe2 cards can only drive 520/528 Byte block drives.
PCIe3 cards can drive 520/528 and 4K Block drives.

Thus the internal cards MUST be PCIe3 because even on POWER8 they
support 4K Drives.

so should I ask for the " dual PCIe3 12 GB Cache Raid Plus SAS Adapter
Quad-port 6 gb x8 EJ14. " Paul mentioned?

Not an option. For the internal cards the connectors are significantly
different. Some front and some rear. On POWER9 these sit smack in the
middle of the planar board so you couldn't put EJ14s in there.

Regarding the RAID configuration: would two RAID5 sets of 9 SSDs (8 plus

1

Hot spare) be a good configuration ?

I believe yes. That way each card controls half the drives for best
performance. If all 18 were one RAID set then one card would be idle.

and last but not least, what about the " these (Mainstream) drives are
designed for *workloads with modest write requirements..".

Well there are two flavors of SSD today for POWER. The Enterprise and
the read intensive.

The Enterprise are rated (From memory!) 10 DWPD while the read intensive
are rated only 1 DWPD.

What that means if you've not followed DWPD ("Drive Writes Per Day") is
that a 1TB Enterprise drive can accept 10TB (entire drive capacity x 10)
writes each day for 5 year life. A 1TB Read intensive units then can
only accepts 1TB of writes per day for 5 years.

Back to the performance data to see what your write traffic is. Because
the Read Intensive units are much cheaper and also larger you might be
able to over configure (capacity wise) a fair bit and then live with
those drives instead of Enterprise. But if you write a lot then that
might not work for you.



- Larry "DrFranken" Bolhuis

www.Frankeni.com
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