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.
Creating Volume Sets
Volume Sets are set up with the MOUNT/BIND command.
The qualifier value, volume-set-name, specifies a 1- to 12- alphanumeric-character name identifying the volume set. An ISO 9660 volume-set name can be from 1 to 128 characters in length.
OpenVMS requires volume-set names to be unique in the first 12 characters. In addition, if the first 12 characters of volume-set name are the same as the first 12 characters of any volume label, a lock manager deadlock will occur. To avoid this problem, you must override either the volume label (by using the /OVERRIDE qualifier) or the volume-set name (by using the /BIND qualifier).
You must specify the /BIND qualifier when you first create the volume set or each time you add a volume to the set. To dismount an individual volume of the volume set, you must use the DISMOUNT qualifier /UNIT; otherwise, dismounting an individual volume dismounts the entire volume set.
When you create a volume set, the volumes specified in the volume-label list are assigned relative volume numbers based on their positions in the label list. The first volume specified becomes the root volume of the set.
When you add a volume or volumes to a volume set, the first volume label specified must be that of the root volume, or the root volume must already be on line.
Note that if you attempt to create a volume set from two or more volumes that already contain files and data, the file system does not issue an error message when you issue the MOUNT/BIND command. However, the volumes are unusable as a volume set because the directory structures are not properly bound.
If you mount an ISO 9660 volume using the /SYSTEM or /CLUSTER qualifier, and the volume label is not unique within the first 12 characters, you must supply an alternate 12-character volume label using the qualifier /BIND=volume-set-name. If you choose this option, then Mount verification is disabled for the device.
Dissolving Volume Sets
Once a volume is bound into a volume set, it cannot easily be unbound. To unbind a bound volume set (BVS):
1. Do an image backup of the BVS. 2. Initialize all volumes of the BVS. 3. Do an image restore to a single volume with the /NOINITIALIZE qualifier, or do a nonimage restore to a single volume.
The following command creates a volume set named LIBRARY. This volume set consists of the volumes labeled BOOK1, BOOK2, and BOOK3, which are mounted physically on devices DMA0, DMA1, and DMA2, respectively:
$ MOUNT/BIND=LIBRARY DMA0:,DMA1:,DMA2: BOOK1,BOOK2,BOOK3
The following command creates a volume set with the logical name TEST3. The volume set TEST3 is not shadowed, however each element of the volume set (TEST3011 and TEST3012) is a shadow set, providing redundancy for the volume set as a whole.
$ MOUNT/BIND=TEST3 DSA3011/SHADOW=($1$DUA402:,$1$DUA403:), DSA3012/SHADOW=($1$DUA404:,$1$DUA405:) TEST3011,TEST3012 TEST3