System Programmer Reference › Managing Tape and DASD Resources › Handling Tapes and DASD Resources for Backup and MPC Jobs › Tape Chaining

Tape Chaining

By default, CA VM:Backup writes tape chaining information in the trailer labels of tapes it uses in backup and MPC jobs. When the first tape to use in a job is mounted, CA VM:Backup writes the volser of the next tape to use in the first tape's trailer label. CA VM:Backup repeats this process for each subsequently mounted tape so that each tape in the tape set points to the next tape:

Tape chaining information is used by:

• CA VM:Backup when restoring data.
• The VMBRITS utility when restoring CA VM:Backup.
• The VMBSCAN utility to produce its reports.

At sites that use ACLs and preload general scratch tapes rather than supplying the tapes selected by CA VM:Backup or CA VM:Tape, CA VM:Backup has to remount tapes to correct tape chaining information already written in their trailer labels. You can avoid these remounts by preventing CA VM:Backup from writing tape chaining information in backup tape trailer labels.

To do so, you must also do the following:

• Include a TAPECHAIN NO record in the VMBACKUP CONFIG file. For more information, see TAPECHAIN Record.
• Interface CA VM:Backup with CA VM:Tape. CA VM:Backup writes tape chaining information in the CA VM:Tape TMC; if this information is not available from tape labels, CA VM:Backup must be able to obtain it from the TMC to restore data.
• Implement the CA VM:Tape AUTOPICK facility with AUTOPICK ACCEPT specified. The AUTOPICK facility lets CA VM:Tape pre-select the next scratch tape and pass the volser to CA VM:Backup during a backup job. The ACCEPT option lets you preload general scratch tapes instead; CA VM:Tape updates the TMC with the correct volsers.

  Important! The operator must not issue the AUTOPICK STOP command during backup or MPC job processing.

• Know which tapes to mount in the event of a site disaster. VMBSCAN and VMBRITS cannot reference the CA VM:Tape TMC, so you are responsible for providing this information.
• During backup jobs, set up the ACL to run in AUTOMATIC mode. You can return the ACL to SYSTEM mode after the job completes. (Under normal circumstances, CA VM:Tape requires the ACL to be in SYSTEM mode.)