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FAST Pool and Mixed Disk Capacities
Should I mix FC400 and FC600 disks in a Pool?
I have a mix of FC400 and FC600 drives in my NS-480 Unified array. I am planning a migration from traditional RAID groups and MetaLUNs to FAST Pool(s). All of my FC400 disks are currently allocated, so the FAST pool will initially contain (only) FC600 disks along with SATA and EFD. When I migrate the MetaLUNs out of the RAID groups into the Pool I will reclaim the FC400 disks. Would it be better to create a separate pool containing the FC400 disks rather than adding them to the pool that already contains FC600 disks?
jps00
392 Posts
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January 13th, 2011 12:00
Nothing is going to stop you from doing it.
However, its not a Best Practice. The two different drives are going to have similar, but not the same performance. So your response times are going to be more varied depending on which drive-type RAID group an LBA has landed on.
If you want my opinion, I'd create two pools, LUNs for each on a different SP.
EMC CLARiiON Best Practices for Performance and Availability FLARE Revision 30.0 in its 'Storage Pool Size' section contains a longer discussion of pool Best Practices. Best Practices is available on Powerlink.
kenn2347
542 Posts
1
January 13th, 2011 12:00
I have looked thru the EMC FAST for Clariion WP and it doesnt say anything about NOT having 2 different size disks in a FAST pool. I dont know what would happen if you added the 400G drives at a later date (In groups of 5 per best practice).
From what i have read around these forum is that when you add more disks to a pool with the expand command, it does not restrip everything across the additional spindels like it does on the SYMM series. So you dont really gain any performance. It takes those new disks and creates what i refer to as a seperate raid group/pool inside your existing pool and if you need to add a lun then it makes sure that the whole lun will only be used by that new space. It wont span it over to the existing pool if some data is placed on it. You also have no control on where on the tier of storage of a pool to place your lun.
I think i confused myself here...
IF you create a seperate pool for the 400G drives, it will just be a normal pool unless you have spare EFD or SATA to make it another FAST pool.
JWeland
6 Posts
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January 13th, 2011 16:00
Thanks JPS. Found the info in the best practices document - I had looked there prior to posting but missed it somehow. I hadn't yet considered that a pool is assigned to an SP, I will most likely be going with at least two pools based on FC disk capacity.
jps00
392 Posts
1
January 14th, 2011 07:00
I was imprecise in writing about separate SPs. Its the LUNs that need to be on separate SPs, not the pools. My bad.
JWeland
6 Posts
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January 16th, 2011 13:00
That makes more sense - thanks for the correction.