I entered the following with following results:

fs2:/etc/amanda/fullback # amtapetype -o -t LTO4 -e 800g -b 2048k -f /dev/nst0
Writing 4096 Mbyte   compresseable data:  48 sec
Writing 4096 Mbyte uncompresseable data: 44 sec
Estimated time to write 2 * 819200 Mbyte: 17600 sec = 4 h 53 min
wrote 401408 2048 Kb blocks in 98 files in 8504 seconds (No space left on 
device)
wrote 401408 2048 Kb blocks in 196 files in 8799 seconds (No space left on 
device)
define tapetype LTO4 {
    comment "just produced by tapetype prog (hardware compression off)"
    length 802816 mbytes
    filemark 0 kbytes
    speed 95049 kps
}