Larry,
Thanks for the input.
Here's the link for the performance issue. Search " Including disk units in a parity set"
http://www-01.ibm.com/support/knowledgecenter/ssw_ibm_i_71/rzaly/rzalyincludedpy.htm
Attention: 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. The degradation can occur because the adapter uses firmware in place of specialized hardware assists when drives are included into an existing parity set. For this reason, the Include disk operation is no longer recommended with PCIe2, PCIe3, and newer generations of SAS RAID adapters. Systems with POWER8(tm) technology and beyond do not allow the Include disk operation. Alternatives for adding disk units to the system are to stop parity on the existing set and then start parity with the additional disks in the set, or to create a new parity set of three or more disks with the additional disk units.
As far the life of the EXP24S, this is the only drawer IBM is still supporting on P8.
The newest SSD drives are Gen3, but the EXP24S is only Gen2. I worry that when newer drives appear, EXP24S may not support them.
Why was the EXP30 drawer never made available for the I, I thought that was a nice IO drawer in 1U.
Sue previously mentioned that number of raid sets should always be even. I can see why.
One parity set is primary on each 5913, the second parity set is primary on the 2nd 5913.
In my config, I have each 5913 in a separate 5877 PCI drawer, and each drawer is on a separate GX++ loop, for total redundancy.
If I have a loop, PCI drawer, or 5913 failure, there is a redundant backup.
Parity set optimization for RAID 5 protection
Performance
Parity sets optimized for performance provide the fastest data access. The IOA may generate more parity sets with fewer numbers of disk units. For example, if an IOA had 15 disk units and is optimized for performance, the result might be three parity sets with five disk units each.
When in a dual storage IOA configuration, the system attempts to create an even number of parity sets. An even number of parity sets distributes the workload evenly between a pair of adapters which are in a dual storage IOA configuration. This provides the fastest data access since each adapter has a piece of the workload.
If I went with 775 SSD, losing 2 units to parity.
12 775 SSD, DASD% from 2844 to 10,850, Cost 12 x 6200 = $74,400.
8 775 SSD, DASD% from 2844 to 4650, Cost 8 x 6200 = $49,600.
When redoing, I would consider hot spare, Sue previously mentioned you only need 1 per drawer, not per parity set.
Note: The hot spare disk units are not designated to any particular parity set. The hot spare disk unit protects the first failed disk unit that has parity protection, is the appropriate capacity for the hot spare disk unit, and is under the same IOA as the hot spare disk unit.
Paul
-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of DrFranken
Sent: Sunday, December 28, 2014 10:14 PM
To: Midrange Systems Technical Discussion
Subject: Re: P7 740 E6C EXP24S mode 1, disk upgrade options
You have summed up the options quite well I would say.
First question is do you have a link to the information where your quote about "large performance degredation" would occur. I have heard this mentioned but not heard of anyone experiencing this. I have added drives to RAID sets on MANY of these adapters and not noted any of the suggested degredation. That said I can certainly see where adding a significant number of drives to a RAID set that currently has only 3 or
4 drives might be a problem.
I suspect Sue could chime in here with additional information on the newer SAS RAID cards. Perhaps memory or other issues internal to those cards could contribute to a performance hit.
As to any new hardware coming nobody who knows will be free to say, so.... :-)
As to the EXP24s being "old" I'm not worried. They are still making that same model and so far as I know have no plans to stop that. It's effectively the same drawer as many of the StorWize SANS too. It is exceptionally unlikely to fail just because it hit 4 years old.
As to mixing SSD and Spinny disk in one 5887 that will work but as the Mythbusters say "Don't do it!" Your very speedy SSDs will end up waiting in line for I/O with your nowherenearlyas speedy Spinny drives. Bad Bad.
Rather like getting behind an 18 wheeler in your Charger Hellcat in a no passing zone. You really should not even mix Spinny and SSD on the same RAID adapters!
Swapping the 177s for 775s seems like a good deal from a maintenance and power standpoint. Keeps you in 1 EXP24s and one set of SAS RAID adapters. You'll really want to end up with TWO RAID sets of 775s so Add a set of 6 with no hot spare to start, move the data to those, then add
8 more for another set of 6 in a RAID set and 2 for hot spares. There, you've doubled your storage, and left room for more later.
Agree that messing with a few spinnies makes no sense and requires another set of cards and a drawer so pretty expensive for just a few drives.
- Larry "DrFranken" Bolhuis
www.frankeni.com
www.iDevCloud.com
www.iInTheCloud.com
On 12/28/2014 5:52 PM, Steinmetz, Paul wrote:
Currently have 18 177 SSD in a 5887 EXP24S mode 1 , with dual 5913.
CEC already used for other LPAR, and I would not use CEC for Prod.
Would like to add disks, either SSD and/or HDD.
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.
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"
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.
Another concern is the age of the 5887 EXP24S GEN2. Announced 4/12/11, will be 4 years old.
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'm really frustrated with this decision, not many good IO options available.
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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