Regarding storage tiering, in high performance environment with ZFS filesystems it is encouraged not to use it.
It also advised not to use data pools if you have any since storage will stripe across all the disks in pool.
Plain luns with only raid protection on storage level as vdevs for zfs pools.
Of course, you will have to take into account amount of spindles in such setup as well as RAID protection level.
Best would be to leave ZFS to do everything on JBOD, but that not feasable with high end storage
For additional performance SAN tweaking with preferred paths (or some other algorithm, not round robin ) per disk can help in some situations.
Check out this document :
http://www.oracle.com/technetwork/se...-wp-167894.pdf
It is for oracle database, but explains alot of things ZFS related and can be used in other scenarios (SSD usage as mentioned).