Technical data

Managing Storage Media
9.7 Mounting ISO 9660 Volume Sets and Groups
For more information about ISO 9660 volume structure on CD–ROM media, refer
to the Guide to OpenVMS File Applications.
9.7.1 Mounting ISO 9660 Volume Sets
ISO 9660 supports volume sets of up to 65,535 volume set members. At any one
time, users can mount a 255-member subset of the total volume set of 65,535.
If your volume set is greater than the number of CD–ROM readers available to
you, you can swap volume set members, for example, as you might when you
have a single reader with multiple volume set members.
9.7.2 Mounting ISO 9660 Volume Groups
A volume group consists of one or more consecutively numbered volumes within
a volume set. Affinity between the members of a volume group is established
by the fact that the volumes are recorded together and are subject to the same
maximum-volume-set-size parameter.
Each volume in a volume group contains information describing all the files
and directories recorded on all of the volumes in the volume set, up to and
including the members of its volume group. For example, assume that a volume
set includes two volume groups:
• The first group includes Volumes 1 and 2, which were recorded together, prior
to the second group.
Volumes 1 and 2 each contain information only about their volume group;
they have no information about the volumes in the second volume group.
• The second group includes Volumes 3, 4, and 5, which were recorded together
at a later date.
Volumes 3, 4, and 5 each contain information about all of the volumes in the
volume set, including Volumes 1 and 2.
How to Perform This Task
When you mount a volume set, you must first mount a member of the highest-
numbered volume group (the most recently recorded group—in the example,
Volume 3, 4, or 5), because only a member of the highest-numbered group has the
information needed to mount all members of the volume set.
If you do not follow this requirement, you must dismount all of the volumes and
start again by specifying a member of the highest-numbered volume group as the
first volume to be mounted.
9.7.3 Handling Partially Mounted ISO 9660 Volume Sets
OpenVMS systems support partially mounted ISO 9660 volume sets. Data is
usually read from all mounted volumes in a manner that is transparent to the
user program.
When a volume-set member is not mounted because the volume set is partially
mounted, OPCOM sends a message to the OPERATOR class DISK requesting
that the unmounted volume be mounted. If you do not honor the request within a
specified time period, or if you do not enable the option to provide for dynamically
mounting a volume, the I/O process fails, and an error message is issued.
9–48 Managing Storage Media