About the SPC-2 SCSI reserve process
The NetBackup process issues an SPC-2 SCSI reserve command to the tape drive that contains the media. (The process can be bptm, bprecover, or bpbackupdb.) If the device is not reserved, NetBackup acquires a reservation. The drive does not process commands from any other host bus adapters (HBAs) until NetBackup releases the reservation or the reservation is broken. If the reservation fails, NetBackup fails the job.
The reservation does not prevent other applications on the host that has the reservation from using the same device and from causing data loss. For example, if a user on the same host issues a UNIX mt command, the mt command can take control of the drive.
After the NetBackup process finishes with the media, it issues an SPC-2 SCSI command to release the reservation during the unmount operation. The release frees the device for access by another HBA.
SCSI reserve does not provide a method to determine if a device is reserved. Only the reservation owner (the host bus adapter) can release the reservation. However, these limitations do not interfere with NetBackup operations in most environments.