I am playing with this as I write as I am in a similar situation. The database that i have resides on one disk array. Given that the BCV works on disk arrays (I am using HP UX XP 256) copying from one disk array to another (more speciifcally, from mount point to mount point), there is not much choice for me other than putting the whole database is backup mode at one time. I can see the value in doing one tablespace at a time (this is a better choice IF your database is of a size for it - mine is only 40 gigs right now). And yes the backup mode is independent of the disk subsystem so it doesn't care how the disks are setup. Also, because of the size of the database and the amount of activity occuring on the system (we plan to do this at night when activity is very low) the database will be in backup mode for 5 minutes so this window is very small and a minimal risk for us.

Just some things that I have encountered so far from my end.