I need advice going forward on our 3PAR 8400 4 node.
It has 4 cages in total (including the ones with the controller nodes).
We initially bought it with 48 3.84TB SSD drives and are running RAID5 7+1 (magazine availability). We subsequently expanded the system by 8 disks now total of 56 Disks and remained on RAID5 7+1.
This is now an unbalanced system.

We are going to expand the system again with another 8 disks and we will have 64 disks in total. This makes me consider my options.

I prefer to change the RAID layout to RAID6 for better resiliency (even though we never had any disk failures). I could go for RAID 6 14+2 without loosing any usable space compared to the current RAID level.

Would this be a good idea?

However, if and when we need to expand again the next balanced configuration is with 96 disks which is too big a jump for the money men

How big a deal is it to run the system unbalanced anyway?

What would you guys do?

Thank you

I would say go for RAID6. You’re not really unbalanced from a hardware point of view with 56 drives, all cages have 14 drives. The number of drives per node doesn’t add up to the set size, but that is a very small problem.

Why? You add two drives to each of your 4 cages.

Yes all cages will get equal share of disk but if I run RAID 6 14+2 there will be a unbalance with regards to node ownership of disk and RAID distribution.

I will have 64 when I expand the disk now. This will allow a balanced RAID 6 14+2. The next number of disk is 80 if i insist on a keeping it balanced.... but If I only buys 8 more it will be unbalanced. But is this a big deal?

Remember that 3PAR looks at chunklets and not physical disks when growing. You have a balanced system from a hardware perspective (identical config behind each node, identical per backend port DP1/DP2 and identical per cage). You don't have a config per node to match your set size, but with a set size of 16 and 4 nodes you would need a multiple of 64 to stay perfectly alligned there. With SSDs that just isn't reasonable and not really a big issue anymore as it is unlikely that you are going to max the SSDs. If you were even close to that you would have a bigger issue with 8400 and not 8450 vs not writing full sets.