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storage pool expansion advice
Our capacity pool is full and we have max'd out the drives on our VNX 5300. We have 8 SAS drives unbound but the first 4 are the VNX operating system (Bus0/Enc0/Disk0-3)... they don't actually show up in the Capacity pool properties when I try to expand it. I only have the 4 SAS Bus0/Enc0/Disk4-7...268Gigs drives. I have 3 NL drives as well at 2TB each that I can see if I do a "Manual" expansion. You can't include them in a 5 disk arrangement, the VNX greys out the "OK" button if you even contemplate it. If I try to expand with just the four disks I get a warning: "Best Practices suggest that for optimum performance for the RAID configuration, the number of SAS disks chosen for RAID5 should be a multiple of 5. If you do not select a multiple of 5, some portion of the pool will not match the specified RAID configuration. Do you want to continue?" I have 2 SAS drives (along with some SAS Flash and NL SAS) as hot spares. They are in different enclosures. I am not really feeling cannibalizing the hot spares. I can migrate a LUN to another storage pool but the other pool is down to 4 TB's and that only delays the inevitable question on what to do with the 4 disks. Are there any thoughts on how to work this out? Should I do a four disk expansion?
Jim_Hegner
212 Posts
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September 9th, 2014 09:00
The vault drives ( Bus0/enc0/disc0-3) cannot be added to a pool, on the VNX5300, if you have any spare capacity there you can utilize it as a traditional raidgroup, be hitting those 4 disc with large amount of IOPS can slow down your whole system.
You do not state how your current pool is setup, the thing we would like to know is how the private raidgroups are in the pool you want to expand...
But the warning is to tell you that id you add disks to a already configured pool, you should always add them equalt to the amount of discs in a private raidgroup...if you add them with fewer discs that data on this raid group will have less performce that the other data in the pool.
tkae the 3 NL-SAS discs you have, they could be added to the Pool ( if you are already running R5 on NL-SAS tier) in R5 2+1 config, the rest of your pool will most probaply be running R5 4+1 or 8+1...so data landing on your new private RG only have 3 disk to support it, where data on the others have 5 or 8 discs to support it...this could get you into all kind of trouble performance wise.
So my advise would be DONT,
and do not fool around with HS, the Hs are there for a reason...
tech1trader
9 Posts
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September 9th, 2014 10:00
Our capacity pool is NL 6+2 and SAS 4+1.
I don't have to make any immediate decisions but at some point I may. I am trying to get ahead on the decision tree.
I may just migrate a LUN to the other pool when the need arises and if that becomes untenable then add the disk in the 3+1 config.
A new SAN is being discussed so this may accelerate the process.
Thanks for your help.
Jim_Hegner
212 Posts
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September 9th, 2014 11:00
Hi Again
If your pool is setup with R6 6+2 for NL-SAS then you have to add all new disc in this tier at the same Raid level, and that will mean R6 6+2.
This means that you cannot use your 3 Nl-sas discs for anything in your pool as the lowest POSSIBLE disc count would be 4, and the recommended is 8.
You can do lun migrations from one pool to another, no problems, just make sure that the applications "living" in the pool being migrated to can live with the added IOPS, without being degraded in performance
tech1trader
9 Posts
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September 9th, 2014 11:00
Hey Jim,
Thanks for your replies, It was helpful to think through the process.
I noticed the pool did not like the 3 NL disks. In automatic they would not even show up.
It will accept the 4 SAS drives so my process will be:
1. See if I can clean up some LUNs
2. Migrate the LUN if necessary
3. Add the SAS drives.
Thanks again for your help.