Technical data

Managing Storage Media
9.6 Setting Up Disk Volume Sets
9.6.1 Understanding Disk Volume Sets
A volume set is a collection of disk volumes bound into a single entity by the
DCL command MOUNT/BIND. To users, a volume set looks like a single, large
volume. Volume sets have the following characteristics:
• Files are automatically located anywhere on the volume set that space is
available.
• Disk quotas are enforced over the entire set.
• A single directory structure covers the whole volume set.
Use a volume set to provide a large, homogeneous public file space. You must use
a volume set to create files that are larger than a single physical disk volume.
(The file system attempts to balance the load on the volume sets, for example, by
creating new files on the volume that is the least full at the time.)
If you want several distinct areas of file storage, with different types of users or
different management policies, you must use a separate volume or volume set for
each area. For example, you might want one volume for permanent user storage,
with limited disk quotas and regular backups. You might want another volume
for ‘‘scratch’’ use, which means that the volume has liberal or no quotas and is
not backed up; also, its files are purged on a periodic basis. Each separate volume
or volume set must contain a top-level user file directory for each user who keeps
files on that volume.
An advantage of separate volumes is their modularity. If one of the drives holding
a volume set is out of service, the whole volume set is unavailable because of its
interconnected directory structure. When a drive holding a single volume is not
functioning, only the files on that volume are not available.
A disadvantage of volume sets is the large size of an image backup of a
multivolume set, which might affect your backup schedule. For example, if
backing up each of five separate volumes takes 5 hours in the evening, backing
up these same volumes in a volume set will take 25 hours, which cannot be done
overnight, thus possibly causing a scheduling problem.
9.6.1.1 Guidelines for Creating Disk Volume Sets
When planning disk volume sets, keep in mind the following points:
• You can turn any single volume into a volume set by binding it with a newly
initialized volume. Likewise, you can add another newly initialized volume to
an existing volume set.
• Do not include a system disk in a volume set.
Caution
Do not make the system disk part of a volume set because updates,
upgrades, and optional product installations do not install correctly, and
the operating system will no longer boot successfully.
• You cannot bind two existing separate volumes containing files into a volume
set. (The MOUNT command appears to let you do this, but the result is not a
coherent volume set.)
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