64 TB limit is an old setting. The actual limit on a 5230 is 100TB+ depending on the amount of shelves you have. What you need to avoid using disk across the two different array controllers. If you have two shelves you can do ~71 TB. there are 36 TB raw per expansion shelf and both shelves can be incorporated into an MSDP. There is some overhead on the disk and all so you only get 70 - 71 TB.
I am going to assume you got a 4TB base unit and if so you can convert that to advanced disk or leave it alone but you do not want to add that to the deduplication pool. It is a major performance impactor.
