DSM/Tape Catalog User's Guide

DSM/TC Tape Processing

DSM/Tape Catalog User’s Guide — 520233-008

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Status Changes in a Volume Catalog Entry

The availability of a tape for a read or write operation is determined solely by the status

of its volume catalog entry. With the exception of bad, the entry’s status is changed by

DSM/TC in real time to reflect what is happening to the tape after it is requested by a

DEFINE.

Status Changes for an Input Tape

Tapes used for input already contain one or more files. The tape volumes containing

these tape files have a status of assigned or full. This status does not change back to

scratch until the tape files expire. What happens to the tape in real time is not reflected

by the entry’s status as it is for output tapes.

Because the tape volume is never given a selected status to reserve it until the

operator mounts it on a tape drive, there is a small chance the tape could be used to

satisfy a subsequent request by another application. In this situation, the operator

would see two mount messages for the same tape name and would have to decide

what to do:



Mount the tape for the first message received. Leave the other mount message

pending until the first application finishes with the tape. Then use the tape to satisfy

the pending message.



Mount the tape for one of the messages and use REJECT TAPEMOUNT to cancel

the mount message for the other request. In this case, the second application

receives an error message indicating its open for the input file failed.

Status Changes for an Output Tape

After an application requests a cataloged scratch tape, $ZSVR goes through the steps

described in

How $ZSVR Manages Tape Requests on page 3-9 to satisfy the request.

As those steps occur, the status of the t

ape’s volume catalog entry changes:

1. After DSM/TC determines which t

ape is a suitable scratch tape or verifies a scratch

tape named in the DEFINE, the entry is changed from scratch to selected.

2. $ZSVR detects which tape drive the operator mounted the tape on and connects

the tape drive to the application to complete the request. $ZSVR also informs

DSM/TC that the request is complete. DSM/TC changes the entry’s status from

selected to in use.

3. The application finishes writing a file on the tape and closes it. DSM/TC changes

the tape volume catalog entry’s status from IN USE to ASSIGNED.