Quantum DLT 8000 Product Manual page 127

SCSI Description
NOTE
In contrast to the BUSY status condition, the DRIVE NOT READY Sense Key is
returned as part of the Sense data following a REQUEST SENSE command and
indicates that a media access command has been issued but that the media is not
ready to be accessed. For example, the tape cartridge is not installed, the tape
medium has been unloaded, the tape drive is currently initializing the tape
medium to prepare it for access, etc.).
In the DRIVE NOT READY state, the initiator cannot perform any operation that
would cause tape motion (READ, WRITE, VERIFY, for example). These commands
return a CHECK CONDITION status with a DRIVE NOT READY sense key. The
initiator may execute commands that do not require tape motion or access to the
tape medium, and a GOOD status may be the result.
Quantum DLT 8000 Tape System 3-25