My statement obviously caused some confusion. Time to explain it a little 
further:

1. You must have all explain to select and support the max. 
capacity/compression/highest density. I don't know exactly what will happen if 
you can not select LTO5 as device type. Probably you will just end up with LTO4.

2. If you have a LTO5 tape which was written "with LTO4 density", NO backup 
software will enable you to use it with LTO5 density right away. And there is a 
good reason for that:
A good ;-) BU software will first read from BOT to check for an existing label 
to prevent accidental overwrites. Now, as this is a "read from BOT", the drive 
itself (controlled by FW) will fall back to the density found (LTO4 in this 
case). This means - even if you relabel the tape - it will still have LTO4 
density. Sorry, but tape drives worked that way for at least the last 25 years.

The only way to overcome this behavior is to run an unconditional overwrite:
  - Insert the CORRECT media
  - Once loaded, make sure that LTO5 density is selected (usually the max. 
density is the default)
  - Overwrite the media from BOT with a tool that does NOT try to read first 
(for NW, use the tapeexer utility)
Once again be careful and use the correct tape.
Of course, NW will always write to EOT (if he does not have too many write 
errors).

Clear as mud?

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