T800 adding new disks--using DO to "tune"

[Speedwy]

We have a T800 with 4 drive chassis, 4 drive magazines each (total of 64 drives). I have one CPG, Raid 5 (3+1) that encompasses all 64 drives. I will be adding an additional 8 drive magazines (32 more drives) and I want these drives to be part of the existing CPG. My understanding is that new drives are automatically added to an existing CPG (is this true?). My concern is more to do with rebalancing existing VLUNs to use all the drives once I add those 32 additional drives. I know I can do this with DO, which we do have a license for, but what I'm NOT sure of is how much headroom you need in order to copy all LUN data to span the additional 32 drives. We've got roughly 26 TB of thinly provisioned VLUNs allocated out of 29 TB total. Of that 26 TB allocated we're hardly using any space--only 4%--because we haven't yet deployed those VLUNs for use. So, will I be ok to use Dynamic Optimizer to expand those existing VV's? Does that question even make any sense?

[Richard Siemers]

The CPG defines how new LDs are created within the CPG, it does not edit or change existing LDs already on the system assigned to it (thats what DO does). So after adding 64 new spindles, your data may not touch them unless you do something that creates a new LD, like creating a new LUN, new CPG or have alot of growth on existing LUN/CPGs that triggers new LDs to be created. The chunklets on the new drives will be *available* to the old CPG, unless you edit your old CPG to exclude them... not necessary though imho. If the old 64 drives fill up, it should auto create new LDs for the CPG on the new disks, performance wise, not the best, hence why DO exists.

I suggest creating a new CPG after your install is complete, and using DO to move the LUNs from the old CPGs to the new ones. Sounds like you have plenty of freespace due to thin provisioning, but you can play it safe and compact the old CPGs periodically between DO moves... move a couple luns... compact the old CPG to release that free space, do some more DO moves... repeat. I've noticed that the compact tools and thin reclamation do not recover 100% of the space, they purposely leave freespace allocated to LDs and CPGs, I assume its so future growth will be contiguous. That said... once your old CPG is empty... delete it to free it all back up.

Under the IMC preferences there are some advanced settings to show LDs if you want to poke around and look deeper into your CPGs.

Hope that helps!

[Speedwy]

Thanks so much Richard! So it sounds like once I add those 32 new drives I will create a new CPG that encompasses all physical drives (the original 64 plus the new 32), then slowly migration the existing LUN on the old CPG to the new CPG. I'm still trying to wrap my head around CPG vs. EVA Disk Group.

[ernique]

Hi

I am going to be adding a new mag of disk to an excisting CPG as well. My question is can I use "DO" to balance the excisting CPG into itself instead of creating a new CPG? I am not goingto be able to fill up the current frame with new disk all at once, its going to be a pice meal aproach and I would hateto have to create new CPG everytime I add a new disk Mag.

Your thoughts
ECB

[rmurtagh]

I am not aware of any way to "level" an existing CPG. New LDs will be created on the new spindles, but all existing data will just stay put on the original spindles. Using DO is a workaround to force the data off the old LDs onto new LDs, and to do that you have to move it to a new CPG.

Note that the new CPG can have exactly the same settings as the old one. You don't need to change RAID levels or anything, just as long as it maps to all spindles if the same tier (which is the default AFAIK).

You do want to run compact on the old CPG as you move stuff off to get it to release the old LDs, so that you can reuse those chunklets for your new LDs. Not doing this may end up with your new LDs biased towards the new spindles and may force your new LDs to be located mid-platter rather than the preferred "faster" tracks.

If you are coming from an EVA background some key things to remember:

• Unlike Disk Groups, a single physical disk can belong to more than one CPG.
• LUNs in a CPG are not actively levelled. New allocations tend to cause an overall levelling effect by biasing the new data on the new spindles. This results in old data on old spindles and new data on new spindles, and not all data on all spindles.

[Richard Siemers]

Only thing I can add to that is once you DO all your old VVs to the new CPG, you can even rename the CPG to be the name of the old/removed one... in case cosmetics count =)

[dontke]

I might be late in replying to this but might be helpful for anyone with this issue still...HP 3Par now has system tuner for the F/T/V class inserves which autonomically rebalances/tunes your system when you do an upgrade. This might be much better than deleting and creating new CPGs.

Here is a link for this license

http://h18006.www1.hp.com/storage/softw ... index.html