There is no real reason I'm aware of to have the same number of SAV devices as VDEVs.  The main thing you want is the SAV pool spred wide and evenly across the backend drives of the same class.  If you have all one drive type, the best case senario is the same number of SAV logicals on every physical in the system.   Also RAID1 is highly recommended for the pool.  The SAV pool will see a 100% write workload when first activated.   The performance of the system won't be good if the SAV devices hit device or system WP limits.
I'm going back through my fuzzy memory and I'm thinking I've heard two different stories on save devices for timefinder snap.  As Netbackup currently has no support for Oracle 11gR2 (it doesn't error it crashes) which our development requires this really new version due to some of the new XML features.  They are asking optional backup protection methods from me (with the knowledge it's not the same as being in a different device and/or offsite).  Snapshots seemed the obvious thought as the database is going to be ~20TB of thin devices, in and almost add-only environment with little to no change of the data after inserted (other than the standard Oracle stuff: redo, index branch blocks, etc).   I could swear I remember reading a document that says that for performance reasons you should have at least one savedev for every vdev; but I also could swear I've seen something that the savedev should simply be made as big as possible with no mind to the number of vdev's (like a tdev to datadev).  Without doing the smart "talk to my local performance guru" task, anybody know which one it is?  Environment is DMX4, running 5773
Vdev to savedev ratio?