I'm fortunate to have a Quantum SDLT220 tape drive, and found that mt-st doesn't
know the proper density code.

mt-st version:

XYX:util0:/local/work> rpm -q mt-st
mt-st-0.6-1

/dev/nst1 is a Quantum SDLT220 tape drive:

XYX:util0:/local/work> mt -f /dev/nst1 stat
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x48 (no translation).
Soft error count since last status=0
General status bits on (41010000):
 BOT ONLINE IM_REP_EN
 
It understands my Exabyte M2 drive:

XYX:util0:/local/work> mt -f /dev/nst0 stat
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 1024 bytes. Density code 0x28 (Exabyte Mammoth-2).
Soft error count since last status=0
General status bits on (41010000):
 BOT ONLINE IM_REP_EN

No big deal; the drive still works fine.