MSA 2062 (And all 6th gen) disk group choices

[jwoods483]

I have a reasonable amount of experience on the 4th gen MSA SANs.  (Mostly the 2040.)  I'd generally opted to use linear disks in the past to make expanding vdisks easier.  That's no longer an option on the 6th gen SANs.

I have my head wrapped around how the pools work and I've also read up on MSA-DP+.  Unfortunately, I don't have 12 disks to work with, so that's not an option.  In the past, I've always used RAID 10 for magnetic disks, and my intention was do that here as well.

But then I got to thinking: if the pool is going to split my data proportionally across each disk group (of the same performance tier) in the pool, would I get the same performance as a RAID 10 by instead adding multiple mirrored pairs (RAID 1)?  That is to say, a RAID 10 is a stripe of mirrors, so wouldn't a pool with many mirrors be essentially the same thing?  And then, in the future, if we needed to add storage to the pool, it would be easy to just add a new mirrored pair and not worry about upsetting the balance of IOPS across the spindles.  Am I making sense?

[JonPaul · Accepted solution]

@jwoods483 
By using many RAID 1 in the same pool (Wide Striping) you will end up with the same basic data distribution as using a single RAID 10.  Mirrored then striped.   But you are exchanging 1 limitation for another.
There are a maximum of 16 disk-groups allowed in a single Pool (MSA Storage Management Guide, pg 141)  https://www.hpe.com/psnow/doc/a00105312en_us
Which would limit your pool to 32 drives (16x RAID 1 disk-groups) but you would be able to expand incrementally by RAID 1 sets.
By using a single RAID 10 you could expand to 16 disk-groups of 16 drives (Physical limitation of 240 drives would kick in before that) but your expansion would be in 16 drive increments.
Maybe there is a happy middle ground you could find of multiple RAID 10 of fewer drives.
Note that when you expand a Pool by adding a disk-group there is some time where the extra capacity will not be available as the Pool will re-balance the data across the disk groups first.  

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System recommended content:

1. HPE MSA 2062 Storage Array - Overview

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[Sunitha_Mod]

Hello @jwoods483, 

We do see you have marked the reply as solved. We are glad to know your concern has been addressed.