Technical data

Managing Storage Media
9.8 Mounting Tape Volume Sets
The operating system supports the continuous processing of mounted volumes
in a tape volume set through automatic volume switching and automatic volume
labeling (AVL).
9.8.2.1 Creating Labels
Depending on the following conditions, the file system does or does not create a
label:
• If the file system is writing to the volume set, it creates a label for the
magnetic tape and initializes the tape with that label and the protection
characteristics set for the first volume of the volume set.
• If the tape file system is reading the volume set, it tries to mount the next
tape in the volume set with that label.
• If the drive has no tape loaded on it, or the wrong tape, the tape file system
sends a message to the operator console notifying the operator either to mount
a tape or to mount the correct tape.
Before processing continuation volumes, the tape file system processes the
protection on that volume (as described in Section 9.4.2). If the file system
determines that the user does not have access to the volume, it sends a message
to the operator.
The label fills the six-character volume identifier field:
• Characters 1 to 4 of the field contain the first four characters of the label
specified for the previous volume in the volume set. (If the label is less than
four characters, the volume identifier field is padded with underscores; for
example, if the volume identifier is XXX, the padded field is XXX_.)
• Characters 5 and 6 contain the relative volume number for that reel in the
volume set.
Note that the system can generate only 99 unique labels for a given volume set.
With automatic volume switching enabled, the operator can load a tape on the
next drive allocated to the tape volume set anytime before the volume being
processed reaches the EOT mark. The tape file system mounts and initializes (if
INITIALIZE was specified originally) the next tape in the volume set and then
notifies the operator that the switch has occurred.
9.8.2.2 Enabling Automatic Volume Switching
To use automatic volume switching, you must allocate more than one tape drive
to your volume set. After you do so, the tape file system switches volumes for you
automatically by selecting the next tape drive allocated to the volume set. The
tape file system expects you to load the next volume in the volume set on that
drive.
Examples
1.
$ MOUNT MUA0:,MUA1:,MUA2: TAPE
In this example, the volume with the identifier TAPE is mounted on the
MUA0: drive. Load continuation volumes for this set on the tape drives in
the following order: MUA1:, MUA2:, MUA0:, MUA1:, MUA2:, and so forth.
Managing Storage Media 9–53