PEND-TLD always for all media servers and 1 drive after rebot

You can certainly try those.

For SPC-2 reservations, only the HBA that made the reservation can release it - so if the reservation was made for example by a media server that is now down/ removed/ unwell ....  you cannot release via commands.

I recommend using persistent reservation, this uses a numeric key, we know if we made the reservation ( the key is held on the drive firmware/ memory) and so any HBA can make it.  If we do not recognize the key, we won't release it (for example, if it was made by some other application ... which would be bad, but ...)

The golden rule:

All devices (media servers , ndmp hosts etc ) that share a drive MUST use the same type of reservation.  If you have some using SPC2 and others persistent, you WILL get data loss at some point.

Persistent reservation is more intellegent, it can also offer slightly more ways to troubleshot (using for example the sg_utils 3rd party commands).

Tried 

root@host1# mt -f /dev/rmt/3cbn forcereserve
root@host1# mt -f /dev/rmt/3cbn status

And now all is OK, drive is working. Thanks for help!