VNX FAST VP and FAST CACHE

I am trying to set up FAST VP and FAST Cache in my VNX array.

I am not understanding if I should be creating a single Heterogenous storage pool with my flash/SAS/NL-SAS disks or create 3 different homogenous pools.

Can FAST VP function accross multiple homogenous pools or do we have to have a single heterogenous pool?

Thanks!