I replied to your Private Message as well, but since this question shows up for the community as a whole I’ll answer here too.  The net is that the physical form factor of the disk makes absolutely no difference. All that matters is the drive technology (SSD, SAS, NLSAS), Capacity (300GB, 600GB, etc), and the rotational speed (7K, 10K, 15K)  For non-FASTVP homogenous pools, make sure that all disks in the pool have the same technology, capacity, and rotational speed.  For FASTVP heterogeneous pools, make sure that all disks in a particular tier have the same capacity, and rotational speed. (Technology matters here too but FASTVP automatically assigns the correct technologies into their tiers)  Richard J Anderson
According to the FAST VP Best Practices whitepaper it is recommended to not mix 2.5" and 3.5" SAS drives in a FAST VP pool because FAST VP does not acknowledge the different rotational speeds (10K for 2.5" and 15K for 3.5").  I asked a partner support engineer about mixing 2.5" and 3.5" drives in a FAST VP pool and was told it was not supported but no explanation why outside of the rotational speeds.  Can you mix 100GB 2.5" EFDs with 3.5" 2TB 7.2K NL_SAS?  How about 2.5" EFD, 2.5" 10K SAS, and 3.5" NL_SAS?
FAST VP storage pools with 2.5" drives and 3.5" drives?