I am trying to calculate how many drives it will take to backup our data
for a new silo we are pricing out.  The tape drives will be 9840's and I am
using the max speed of 18 MBps which is about 65 Gig an hour?    The formula
I am using looks like this...



                           Backup Data Volume
                     ------------------------------------------
= How many drives you will need
                Tape drive throughput    *    backup window


The speed I rated the 9840 tape drive; is that about 65 Gig an hour?

Are there any other formulas people use to determine how many tape drives
you will need?

Thanks
David