Tape drives are valuable resources under multi-user environment. Drive allocation and mutual exclusion of the device file are essential requirements. We have built a mechanism to allocate a drive using the tape library server software. Only the user processes on the same workstation as the drive can be allocated, while tape library server keeps track of which drive is being used. When the tape handling request comes from a client, it controls the movement of the robot arm, load the tape into the allocated drive, then updates the file index database. The library system also checks whether the tape volume is mounted group-wise. If the drive is allocated and the tape volume is mounted in ``shared'' mode, any member in the same group in /etc/group file can access the tape volume, mount or umount the tape, and deallocate the drive.
Commands mtalloc/mtdealloc allocates and deallocates a tape drive. Once the drive is allocated for a given user UID, a user tape volume can be mounted or unmounted with mtmount/mtumount commands. C and Fortran API functions mtopen/mtclose opens and closes a file on the tape volume, and mtwrite/ mtread API functions writes and reads a data record to/from the tape volume. There are several other commands and API functions such as listing the user file catalog information or handling and reporting error status.
Tape format used in the direct access mode is designed to achieve media portability. Files on a tape volume are separated by a file mark, and all file catalog information are kept on a catalog database at the tape library server. Exported tapes can be read with a single DTF drive workstation without any tape library software. User can rebuild the file catalog information manually at any time.