1) The success of this installation will be totally down to the speed of the network between the two SANs. If that is not fast enough the setup will suck.
2) You should check your stretch cluster configuration is supported by Oracle.
3) You will need a third voting disk, on an independent storage system. Preferably on something like an NFS mount and a different server.
4) In general, Oracle suggest using external redundancy wherever possible, since hardware RAID is typically more efficient than ASM mirroring, so from that perspective, I would use external redundancy, but this doesn't stop you having multiple voting disks and OCR locations, to protect against failure associated with losing a file. Let's say you have two disk groups (FRA and DATA), then you can have an OCR location and a voting disk on each. If you plan to have a normal or high redundancy disk group just for OCR and voting disk, then that's fine also.
Check these out:http://docs.oracle.com/cd/E11882_01/rac ... m#BGBJEBDJhttp://kevinclosson.wordpress.com/2008/ ... tup-right/