We have a cluster with 2 nodes and running on data ontap version 8.3.1 c-mode.
We have two SAS aggregates hosting on each node and raid group size is 17.
We have installed new disk shelf with 24 drives. I want to add the new disks to the exising aggregate. But with the current raid group settings i can able to add only 17 disks to the existing aggregate. Remaining 7 drives will be not used.
I don't want to waste those disks as spares, what i am planning is i want to change the aggregate raid group size to 20 and add the 3 disks to the existing raid group and create a new raid group with 20 disks.
RAID group sizing is always a littel awkward, but you are basically looking for good logical splits.
as one of the responses mentioedn 24 for SAS is not a bad idea, but as you've said it's really about logical bounderies.
nothing wrong with your original idea, make it 20.. add three drives and then a new RG of 20 and add them to aggregate is all fine.
personally i try to keep my boundaries to shelves.. hence 24 a good number, so if i add a full shelf, i'm getting the optimum capacity without drives getting left over.
there are some suggestions around whether you want capacity or resillience, so smaller RG's provide less performance, but in the event of failures have quicker rebuild times etc... but often these aren't huge considerations.
one thing you didn't say was you current setup.. so two 17 drive aggregates, so what is that 36 disks, with 17 in RG's and a couple of spares?
not sure if this all helps.. but your original plan is solid enough, just think of next time you add a shelf.. you'll end up with a similar problem.