a) Yes, we do backup with finer granularity. However, if a RAID group fails, I have to restore the whole thing, so fine granularity does not help much :-(
b) Yes, I am thinking about switching to a 10 disk RAID group, with 2 per volume. That makes for 3 shelves, 2 parity disks, and one hot spare.
c) We have a Gigabit network connection, so the 7MB/sec does seem slow.