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This program requires a VAX C compiler. Perform the following steps:
For additional information, see the comments in the DISKMOUNT.H file.
The following sections discuss concepts related to disk volume sets and explain how to do the following:
| Task | Section |
|---|---|
| Create a disk volume set from new volumes | Section 8.6.2 |
| Create a shadowed disk volume set | Section 8.6.3 |
| Create a disk volume set from an existing volume | Section 8.6.4 |
| Add volumes to a disk volume set | Section 8.6.5 |
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:
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.
When planning disk volume sets, keep in mind the following:
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.
When you mount a disk volume set, the volume label specified in the list must correspond to a device name in the same position in the device name list.
You can bind two or more disk volumes into a volume set. The first volume in the set is called the root volume. Each volume in the set is identified by a volume number relative to the root volume, which is always relative to volume 1.
A disk volume set has a single directory structure. The master file directory (MFD) is on the first volume in the set.
When a disk volume set is on line and mounted, you can access all files and directories in the set by specifying either of the following:
Use the /BIND qualifier with the MOUNT command to create a disk volume set in the following format:
MOUNT/BIND=volume-set-name
where:
| volume-set-name | Specifies a 1- to 12-alphanumeric-character name identifying the volume set. |
The volume set name must be different from all volume labels within the set, and all labels in the set must be unique.
The /BIND qualifier identifies a volume set by assigning it a volume set name that applies to all volumes in the set. The qualifier also identifies the root volume and creates the directory structure for the volume.
When you create files on a volume set, the file system allocates space for the files anywhere on the set, wherever the most space exists. When existing files on any volume are extended, extension occurs on the same volume unless the volume is physically full.
You can add new volumes to a volume set whenever additional space is needed. You can, for example, bind all disk volumes that are mounted into a volume set on a daily basis. Since this set contains all user file directories, users do not need to specify device names in file specifications to access files on any volume in the volume set. In fact, the physical location of a file is of no concern to users of the system.
Note
Do not bind your system disk into a volume set. System software updates and optional product installations do not support volume sets. If certain system files move or extend to other volumes in the set, the system might fail to boot.
You do not need special privileges to create volume sets. However, you must have write access to the index file on all volumes you are attempting to bind into a volume set; this usually means you also must have a system UIC, have the user privilege SYSPRV, or be the owner of the volumes.
The following sections explain how to perform these tasks:
| Task | Section |
|---|---|
| Create a disk volume set from new volumes | Section 8.6.2 |
| Create a shadowed disk volume set | Section 8.6.3 |
| Create a disk volume set from an existing volume and a new volume | Section 8.6.4 |
| Add volumes to an existing disk volume set | Section 8.6.5 |
To create a disk volume set from new disk volumes, follow these steps:
Examples
$ INITIALIZE DUA1: PAYVOL1 $ INITIALIZE DUA2: PAYVOL2 $ INITIALIZE DUA3: PAYVOL3 $ MOUNT/BIND=MASTER_PAY DUA1:, DUA2:, DUA3: PAYVOL1,PAYVOL2,PAYVOL3
$ MOUNT DUA1:,DUA2:,DUA3: PAYVOL1,PAYVOL2,PAYVOL3
The following example illustrates one way to create a shadowed volume set.
$ MOUNT/BIND=TEST3013 DSA3011/SHADOW=($1$DUA402:,$1$DUA403:), DSA3012/SHADOW=($1$DUA404:,$1$DUA405:) TEST3011,TEST3012 TEST3013
This command creates a volume set with the logical name TEST3013. The volume set TEST3013 is shadowed, and each element of the shadowset (TEST3011 and TEST3012) is itself a volume set.
To create a disk volume set from an existing volume and a new volume, follow these steps:
Example
The following example shows how to create a disk volume set (called USERS) from an existing volume. In this example, the volume USERFILES already contains a directory structure and files; the volume is currently located on the DUA1: device.
$ DISMOUNT/NOUNLOAD DUA1: $ INITIALIZE DUA2: USERFILES2 $ MOUNT/BIND=USERS DUA1:, DUA2: USERFILES, USERFILES2
In the MOUNT/BIND command, you must specify the existing volume label USERFILES before the volume label USERFILES2. USERFILES will be the root volume of the set.
Caution
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 enter the MOUNT/BIND command. However, the volumes are unusable as a volume set because the directory structures are not properly bound.
You can add volumes to an existing volume set at any time. The maximum number of volumes in a volume set is 255.
This section contains examples that show how to add volumes to an existing volume set.
Examples
$ INITIALIZE DUA4: PAYVOL4 $ MOUNT/BIND=MASTER_PAY DUA4: PAYVOL4
Examples
$ INITIALIZE DUA4: PAYVOL4 $ MOUNT/BIND=MASTER_PAY DUA1:, DUA2:, DUA3:, DUA4: - _$ PAYVOL1, PAYVOL2, PAYVOL3, PAYVOL4/SYSTEM
To access an ISO 9660-formatted CD--ROM, you can mount disk volumes in two ways:
The Mount utility (MOUNT) builds the I/O database structures that are needed to access ISO 9660 directories and files. MOUNT also verifies the presence of an appropriate ACP to perform $QIO functions specific to ISO 9660. Currently, you cannot mount ISO 9660 media as a system disk. See the OpenVMS System Management Utilities Reference Manual for details.
For more information about ISO 9660 volume structure on CD--ROM media, see the Guide to OpenVMS File Applications.
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.
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:
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.
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.
All ISO 9660 volumes contain a Primary Volume Descriptor (PVD) that uses ASCII (ISO 646-IRV) as the character set. Both ISO 9660 and OpenVMS file naming conventions use the same subset of ASCII characters when displaying the directories and file names of a volume.
In addition to mounting ISO 9660 volumes using the default PVD, you can also mount ISO 9660 volumes using a Supplementary Volume Descriptor (SVD).
This capability allows access to an ISO 9660 volume with directories and file names containing characters from character sets other than the ISO 9660 limited set, which includes only A through Z, underscore (_), period (.) and semicolon (;).
The author of the ISO 9660 volume set must record the volume with the required PVD, and optionally with one or more SVDs. Each SVD must contain a unique volume label and escape sequence.
Use the following command syntax to mount an ISO 9660 device using an SVD:
MOUNT device-name volume-label /UCS_SEQUENCE=escape_sequence
where:
| device-name | Specifies the physical device name or logical name of the device on which the ISO 9660 volume is to be mounted. |
| volume-label | Specifies the SVD volume label obtained from the author's label on the CD--ROM. |
| escape-sequence | Specifies the escape sequence obtained from the author's label on the CD--ROM. |
If an ISO 9660 volume contains SVDs with no escape sequence specified, the default character set is assumed to be ISO 646 (ASCII). This default character set allows the use of the file specification character set supported by OpenVMS, which includes these additional characters: dollar sign ($) and dash (-).
Use the following command syntax to mount a volume using the SVD volume label when no escape sequence is specified:
MOUNT device-name volume-label /UCS_SEQUENCE=""
Note
If an ISO 9660 volume contains SVDs with escape sequences other than ISO 646, ISO 2022 or ISO 13646 (formats on CDs), the character set might not interoperate with the OpenVMS file specification syntax.
Refer to the Guide to OpenVMS File Applications for more information about ISO 9660 volume structure on CD--ROM media.
Table 8-14 describes problems and restrictions that apply to OpenVMS support of the ISO 9660 standard and explains how to resolve them.
The procedure for mounting a tape volume set is similar to the procedure for mounting a single tape volume, described in Section 8.5. The number of volume identifiers does not need to equal the number of device names you specify. In 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 8.8.1 |
| Mount continuation volumes in a volume set | Section 8.8.2 |
| Mount volume sets with automatic switching disabled | Section 8.8.2.3 |
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:
Examples
$ ALLOCATE MUA0: %DCL-I-ALLOC, _MARS$MUA0: allocated $ ALLOCATE MUA1: %DCL-I-ALLOC, _MARS$MUA1: allocated $ ALLOCATE MUA2: %DCL-I-ALLOC, _MARS$MUA2: allocated
$ INITIALIZE/DENSITY=1600/PROTECTION=(G:RW) MUA0: TAPE1 $ INITIALIZE/DENSITY=1600/PROTECTION=(G:RW) MUA1: TAPE2 $ INITIALIZE/DENSITY=1600/PROTECTION=(G:RW) MUA2: TAPE3
$ MOUNT MUA0:,MUA1:,MUA2: TAPE1,TAPE2,TAPE3 TEST %MOUNT-I-MOUNTED, TAPE1 mounted on _MUA0: %MOUNT-I-MOUNTED, TAPE2 mounted on _MUA1: %MOUNT-I-MOUNTED, TAPE3 mounted on _MUA2:
When mounting a tape volume set, follow the general procedures described in Section 8.8.1. Once you create the volume set, you do not need to initialize the volumes when you mount the volume set.
6017P023.HTM OSSG Documentation 22-NOV-1996 14:21:49.92
Copyright © Digital Equipment Corporation 1996. All Rights Reserved.