Re: MetaLUN vs. FAST Pool
It will not get promoted to FAST-cache if it is already on EFD. I'll clarify what I mean:
When you look at both setups, the one setup has a FAST-VP pool (with EFDs there) and some FAST-cache. The other solution has RAID10 (non FAST-VP) with more FAST-cache on top.
Blocks that are on the RAID10 set which get touched once will never make it into FAST-cache, thus never in EFD at all. As opposed to the FAST-VP solution, where the hottest data will actually be sitting on EFD already (on the EFDs in the FAST-VP pool). So isolated reads will come from EFD in this setup, but not in the RAID10/FAST-cache setup.