filesystem throughput measurement

["Douglas A. Tutty" <dtutty@porchlight.ca>]

I'm considering getting a tape drive for intermediate backup and
long-term archiving (e.g. DLT-IV or LTO).  Newer drives require a higher
data rate to keep them fed than older drives.  

I can measure raw hard drive speed with hdparm -Tt, but how do I measure
how fast a backup software could read from the filesystem to know how
fast a tape drive my box will support?

The box is an Athlon64 3800+ on an Asus M2N-SLI Deluxe with 1 GB ram
(one stick only), with two Seagate 80 GB SATA-II drives. 

The system filesystems are on LVM over RAID1 and the data filesystems
are on LVM striped volumes (for better speed).

Thanks,

Doug.