I am trying to backup a VLDB (800+gig) to multiple devices. I am using 4 disk drives. Assuming all devices have the same performance, should the 4 devices fill equally? (IE 200gig per drive) If so, what would might happen if one of the 4 drives only has 100 gig free with the other 3 having 300 gig free each?
There are 10,000 moving pieces in this puzzle... If you define the four disks as one logical drive using RAID, you have no way to tell and no reason to care. If you define the four disks as four physical drives, you can specify what goes on which drive, and tinker to your heart's content.
I would STRONGLY suggest using RAID, and letting the hardware/OS do its job. Device management is an incredibly poor use of a dba's time in almost every case I can imagine.