> Finally the space is used a
> little more efficiently then straight Raid 1 mirroring.

"A little"? The space-efficiency advantage of RAID5 is that it's a *lot*
more efficient than RAID1. For both configurations, the space overhead is
constant:
 RAID1: 50% of the physical drive space
 RAID5: one drive

So, a RAID1 array composed of 10 9GB drives provides 5GB of usable space;
the same 10 drives in a RAID5 array provide 90GB of usable space. Taken to
an extreme, a RAID controller with 4 wide SCSI channels would provide 30 x
(individual drive capacity) in RAID1, or (59 x individual drive capacity) in
RAID5.

Steve