hard disk reliability

[Justin Moore]

Hello,
   I'd be interested to know if anyone has any of the newer, high-end SCSI
drives in the 36 - 47 GB range, and what kind of reliability they've
seen in of those.  The kind of application(s) I have in mind will be very
very heavy on I/O, so these drives definitely will be pounded around the
clock.

   Also what kind of experience have people had with different RAID
levels, mainly RAID 5 and 10?  I've gotten different definitions of what
level 10 is exactly.  The definition from the Quantum page is disk 
striping with mirroring, so the failure of two disks is unlikely to kill
you unless they're the correct (or incorrect, I guess) two.  Given the
reliability of the SCSI drives, would there be a financial advantage in
using this if the data was absolutely irreplaceable?

Thanks.
-Justin Moore