source:
docs.sun.com: Solaris Handbook for SMCC Peripherals
* Your system is able to access the tape drive and a tape cartridge is present, if the following status is displayed:
Archive QIC-150 tape drive:
sense key(0x0)= nosense residual= 0 retries= 0
file no= 0 block no= 0
sense key= nosense indicates that your system was able to access the tape and there were no errors. You can then use any of the backup commands described in the following sections.
* The following information tells you that the tape drive was just reset, powered on, or a tape cartridge was recently installed.
Archive QIC-150 tape drive:
sense key(0x6)= unit attention residual= 0 retries= 0
file no= 0 block no=0
In this case, execute the mt -f /dev/rmt/0 status command again until the sense key(0x6)= unit attention advisory message is replaced with the sense key(0x0)= nosense message.
* If the following status is displayed, your system is unable to access the tape.
/dev/rmt/0: no tape loaded or drive offline
In this case, insert a tape and execute the mt -f /dev/rmt/0 status command again.
Also, to further test have you tried doing a lowlevel tar and restore? I think the device for low level tar should be /dev/rmt/0l or 1l (L)