Well, it kind of depends on your access patterns. For instance, if the vast majority of your your accesses are sequential, it makes sense to set up the drives so that each drive is exported to a seperate lun, with RAID 0 or such for luns that need more storage or performance. If your access is all completely random and you're looking for the most averaged performance (and you don't care too much about guaranteed performance for certain luns), then you should just put all the drives in one big raid set for the best performance. If you have one or two luns that need a guaranteed baseline performance level or are almost completely sequential, then you could just put those luns on a RAID 1 raidset, with the rest in a big RAID 5, 6, or 10 raidset.

How important is the data? Is a once-in-four-years loss of data (where you have to go back to tape or some other backup) acceptable? If not, you should at least do RAID 5, and probably a RAID 10 or 6, especially if you have more than 4 or 5 drives. RAID 6 is going to be more than enough to stop worrying about random drive failures (but you'll still have to worry about batches of drives failing). Also, remember that RAID is not a backup, and volume replication, since it's like a network RAID 1, is also not a backup.

Some of our customers use rotating snapshots so they don't have to always go back to tape if they accidentally delete something, but a snapshot is not a real backup, either. Remember, you HAVE to have a backup that is delayed in time and on completely separate hardware. RAID isn't going to save you if your datacenter is flooded (hello, Fargo!) or a recently-fired employee decides to eject a bunch of hard-drives on your SAN on his last day.