richard612 wrote:
Thanks! One more question if I may... The final goal is to have three CPGs, one for each drive size. How should I handle snapshots? I've read other threads that discuss the virtues of having separate copy CPGs. Should I plan for six CPGs -- one data and one copy for each drive size?
Edit: I just had another idea... Dedicating a subset of the smallest drives to a RAID 1 copy CPG. This would provide a high performance "landing zone" for incoming writes (we have 1 or 2 daily snapshots of every volume present at all times) without incurring the usual RAID5/6 write penalty. Thoughts?
I would create one copy cpg for everything, and put it on the same config as your biggest FC CPG.
RAID1 seems like a waste... Remember that 3PAR does COW, so when you overwrite a block on a volume with a snapshot it will move data to the snapshot and then write the new block. If you overwrite the same block again, it will just write. So you are essentially putting RAID1 on something that will never be read and only be written once (per snapshot). And from a host performance perspective, write ack is given when the new write is written to cache so it doesn't have to wait for the COW to complete. The only penalty is backend.