Relocate Copy CPG

[Josh26]

Hi,

I have a 3PAR 7200.

I have a CPG for FC storage in RAID5.

I have a Virtual Volume using that CPG, and it uses the same for the Copy CPG.

I'd like to store snapshots instead on an NL, RAID6 CPG, in order to better capitalise on the capacity available within our faster storage. Simply changing the setting from the IMC produces an error "Use tunevv to allocate snapshot space from a different CPG".

I have however read a tonne of literature on the tunevv command and have several conflicting options for the right command. Naturally I'd like some clarification before I try any of them.

[Richard Siemers]

You can use the GUI to tuvevv and just relocate the copy space (not the user space) to NL in your situation. Right click the VV and look for the tune option. Follow the wizard, hope this helps!

[yizhar]

Hi.

Raid 6 NL has random write penalty that you can avoid.
I think that if you want to store the copy space on NL disks (copy on write snapshot), then RAID1 or RAID5 will be better choices for that purpose.

Yizhar

[Josh26]

Many thanks Richard, that did the trick.

yizhar, for Nearline drives I'm reluctant to run RAID5, given we're only discussing snapshots that aren't actively utilised by servers I'm quite unconcerned about the performance.

[hdtvguy]

You have to remember that the 3par is COW snapshots, so while the snap may not get access the initial move of the data from the user CPG to the snap CPG will incur the heavy write penalty, if you have a busy volume that has massive amounts of change that is snapped to RAID 6 you will be incurring a lot of IO overhead.

[yizhar]

Hi.

Exactly - as explained above.

The 3PAR will probably do good job and hide that write penalty using caching for example, but it will still affect the NL disks and compete for NL disks IOPS for other volumes (or snapshots) on them.

If you are not happy with RAID 5 on NL for the snapshots, you can also consider RAID 1 .

Again - RAID6 will do the job but with write penalty (that might affect production volumes) that can be reduced by using RAID5/RAID1.

Yizhar