Ean Kingston wrote:

I'm using 40GB DLT tapes (according to the label). Despite what the comment 
produced says, I used the non-compressed device. I didn't give it an estimate 
for the tapesize.

Despite using the non-compressed device, I believe the comment :-)
Probably solaris, isn't it?  You did modify the /kernel/drv/st.conf as
indicated in "man st"?
You loose more than 10% of the tape capacity if using both hardware
and software compression.
And amtapetype would finish faster when given a more accurate speed

of the package, so it doesn't matter).

Writing 256 Mbyte   compresseable data:  34 sec
Writing 256 Mbyte uncompresseable data:  105 sec
WARNING: Tape drive has hardware compression enabled
Estimated time to write 2 * 1024 Mbyte: 840 sec = 0 h 14 min
wrote 1102644 32Kb blocks in 3372 files in 21817 seconds (short write)
wrote 1101228 32Kb blocks in 6756 files in 29828 seconds (short write)
define tapetype HP-DLT1e {
   comment "just produced by tapetype prog (hardware compression on)"
   length 34499 mbytes
   filemark 13 kbytes
   speed 1399 kps
}