MSA Storage

Re: Single pool with MSA-DP+ or two pools with RAID5 or 6?

 
JDDellGuy
Occasional Contributor

Single pool with MSA-DP+ or two pools with RAID5 or 6?

Hello,

I'm new to SAN planning, so I'm discovering a best practice question after already ordering and receiving equipment.

We have a dual controller HP MSA 2062 SAN with 2x 1.9 TB SSD and 12x 1.8TB 10K HDD.

I see that MSA-DP+ is a best practice and 12x HDD is the minimum in order to use that.  However, I see that it's also a best practice to have two storage pools so that the controllers can balance their load effectively.

So I have three options.

  1. I can configure a single storage pool with 12x 1.8 TB HDD in MSA-DP+ and the two SSDs as a read cache.
  2. I can configure two storage pools, each consisting of 5x 1.8 TB HDD in RAID 5, 1x SSD for RAID cache, and 1x spare HDD.
  3. I can configure two storage pools, each with 6x 1.8 TB HDD in RAID 6, 1x SSD for RAID cache, and no spare HDDs.

Net storage capacity is sufficient in any of the three scenarios.

I don't like option 2 because the drives are a bit large in capacity for me to be comfortable with the potential rebuild times, even with a hot spare.

I don't like option 3 because it leaves me without any hot spares.

The only downside I see to option 1 is that it leaves me without good load balancing between the two controllers.

What would you do?

1 REPLY 1
JonPaul
HPE Pro

Re: Single pool with MSA-DP+ or two pools with RAID5 or 6?

Great question.

Short Answer:  Option 1 should be used
The MSA systems are capable of impressive performance on a single controller. So much so that now unless you have all SSDs or more than a 24 drives you will not see an improvement in performance using 2 Pools.  Each Pool is controlled by a controller almost independently, therefore if you have 2 pools you are using both controllers and maximizing the system performance. But if the media on the backend, in your case 12x 1.8TB 10k HDDs and 2x SSDs, is not capable of exceeding the performance of a single controller then you are better off with a single Pool to limit overhead (Parity/Sparing) and as a side benefit when a controller is shutdown for a firmware update or fault the performance of the system will remain consistent, running 1 Pool on the other controller during the shutdown.
RAID 5 is not recommended for spinning media.  MSA-DP+ would be recommended as it has additional features which improve the experience:  Included spare capacity - this is spread throughout the disk-group so that if a drive failed a rebuild starts without a new drive introduced, it also will spread the reconstruct load out to all the remaining disks instead of just one drive getting all the WRITEs. This improves recovery time, with a lot of drives dramatically.  
Expansion is possible - MSA-DP+ lets you incrementally expand your system, as you are starting out with 10 open slots this may be important in the future.
As you purchase an MSA 2062, you also have the included license to allow a performance Capacity Tier (RAID 1 on SSDs).  This would also improve performance over the Read Cache option you describe but I would recommend to start with the Read Cache and see if your performance is where you need. It's an easy task to remove the Read-Cache and re-deploy as Capacity tier, both initially and later.

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