When we make VDI environments, are Fast cache and Extrem I/O still good solution?

I wonder if we use "View storage accelerator (a per-host RAM-based solution), it will solve the problem (I/O bottle neck of storage side) which is a target issue of Fast cache and Xtrem I/O. I found some whitepaper or sizing guide which recommend to use both storage functions.

In what case I sould use which? I'd loke to know the pros and cons.