Technical data

Managing Storage Media
9.8 Mounting Tape Volume Sets
other words, when you mount a tape volume set, you can specify more volume
identifiers than device names or more device names than volumes.
The number of devices you specify directly affects the action taken by the tape
file system when processing continuation volumes in a volume set. For example,
when the number of devices is greater than the number of volumes, the tape files
system requests a continuation volume to be mounted on the first drive from the
list that does not have a volume mounted.
When mounting a volume set, make sure that all the volumes in the set contain
write rings if the user intends to write to any of the volumes in the set. (If even
one of the volumes in the set does not contain a write ring at mount time, all
volumes are write-locked; the system is unable to write to any of them.) Load the
volumes on the drives that have been allocated and place the drives on line.
The following sections explain how to perform these tasks:
Task Section
Create a tape volume set Section 9.8.1
Mount continuation volumes in a volume set Section 9.8.2
Mount volume sets with automatic switching disabled Section 9.8.2.3
9.8.1 Creating a Tape Volume Set
If you do not create a volume set explicitly, the operating system creates one
when necessary. If you have not mounted a volume set and a continuation
volume is required, the tape file system requests that a continuation volume be
mounted and implicitly creates a volume set. For example, if the tape file system
encounters an EOT mark while writing a volume, it sends a message to the
operator console requesting that another volume be mounted.
After you mount the next volume, the tape file system writes the volume and
header labels and then reissues the pending write requests to the continuation
volume. The file-set identifier in the first file-header label of all files written
to the continuation volume is the file-set identifier of the first file on the first
volume. The file-set identifier for volume sets is always that of the first file of the
first volume that is mounted in the set.
How to Perform This Task
To explicitly create a volume set with three volumes, for example, follow these
steps:
1. Allocate devices on which you will load the volumes.
2. Initialize the volumes. Specify the density and the access protection in
addition to the device name and the volume identifier in the INITIALIZE
commands.
3. Mount the volumes, including the device names and volume identifiers.
Specifying a logical name for the volume set is optional. The system not only
confirms which volumes have been mounted, but also indicates on which drive
each volume has been mounted.
The system mounts and verifies only the volumes that are physically loaded
on the devices at mount time. However, the volume identifiers of additional
volumes that you specify are not verified until the volumes are accessed.
Managing Storage Media 9–51