Document revision date: 19 July 1999

You can guard against data loss or corruption by using the OpenVMS Backup utility (BACKUP) to create copies of your files, directories, and disks. In case of a problem---for example, a disk drive failure---you can restore the backup copy and continue your work with minimal disruption.

Information Provided in This Chapter

This chapter describes the following tasks:

Task	Section
Formulating a BACKUP strategy	Section 10.3
Setting process quotas for efficient backups	Section 10.7
Using disks and tapes	Section 10.8
Listing the contents of a BACKUP save set	Section 10.10
Backing up user disks and volume shadow sets	Section 10.15
Restoring user disks and volume shadow sets	Section 10.16
Backing up and restoring the system disk	Section 10.17
Ensuring data integrity	Section 10.18
Troubleshooting	Section 10.19

This chapter explains the following concepts:

Concept	Section
Types of backups	Section 10.2
The BACKUP command line	Section 10.4.1
The Backup Manager	Section 10.4.2
Save sets	Section 10.5
BACKUP file formats	Section 10.6
Volume initialization	Section 10.8.1
OPCOM and volumes	Section 10.9
Multivolume BACKUP operations	Section 10.11
BACKUP tape label processing	Section 10.12
Standalone BACKUP (VAX only)	Section 10.17.2

10.1 Overview of BACKUP Tasks

For BACKUP to effectively guard against data loss, you must back up important data on a regular basis and be familiar with how to restore the data when necessary.

Besides backing up your own files, directories, and disks, you should also back up your system disk. If you have a standalone workstation, backing up your system disk is probably your responsibility. If your system is part of a large clustered computer system, an operator or system manager is probably responsible for backing up the system disk.

The two ways to back up your system disk are:

• Use the menu system described in Section 10.17.1.
• Use a special version of the OpenVMS Backup utility called standalone BACKUP, described in Section 10.17.2. Use standalone BACKUP if you do not have access to the OpenVMS VAX operating system distribution compact disc.

  Note Standalone BACKUP is not supported on OpenVMS Alpha systems beginning with Version 6.1; you must use the menu system provided on the distribution CD-ROM.

Performing an image backup using BACKUP also eliminates disk fragmentation. Fragmentation can occur as you create and extend files on a disk. If the file system cannot store files in contiguous blocks, it stores them in noncontiguous pieces. Eventually, the disk can become severely fragmented and system performance suffers.

To eliminate fragmentation, perform an image backup of the disk and restore the backup copy. When you restore the image backup, BACKUP places the files on the disk contiguously. Alternatively, you can perform a disk-to-disk image backup without using the /SAVE_SET qualifier. This creates a functionally equivalent copy of the entire system disk, on which files are stored contiguously.

10.2 Understanding Types of Backups

Two types of BACKUP operations, file and image, support converting ODS-5 file names to ODS-2 file names. Refer to Section 8.5.5.3 for more information.

10.3 Formulating a Backup Strategy

• The resources you can devote to backups
• The importance of the data
• The volatility of the data

For example, if you have a standalone workstation, a nightly image backup might be your best approach.

Under other circumstances, you might want to choose some combination of image and incremental backups. For example, daily image backups might be inconvenient if your system always has interactive users logged in. You could choose to perform a weekly image backup and nightly incremental backups.

Table 10-1 compares image and incremental backups.

Table 10-1 Comparison of Image and Incremental Backups

Backup Type	Advantages	Disadvantages
Image	Faster to restore than incremental backups. Backs up entire disk.	Uses more space and time than incremental backups. Requires that no interactive users are logged in because of the effect on system performance and because of open file considerations (see Section 10.15.1).
Incremental	Takes less time and media storage space.	More difficult to restore files. Still requires periodic image backups.

You do not have to change tapes or disks during a backup if any of the following statements is true:

• All of the files fit on a single piece of storage media.
• Your site uses a tape loader.
• You have several disk or tape drives available.

In these cases, the backup can be performed by a batch job that runs late at night or at some other time when interactive use of the system is likely to be at a minimum. Section 10.15.7 contains some sample command procedures that you can run in a batch job to back up your disks.

10.4 Understanding the Backup Interfaces

Two interfaces are available to the OpenVMS Backup utility:

• The BACKUP command, which is a command in the DCL command line interface
• The Backup Manager, which is an interactive screen-oriented interface

To back up files, you must specify what you want to back up (the input) and where you want BACKUP to place the resultant save set or file (the output). You can also use BACKUP qualifiers to perform different functions depending upon their position on the command line:

BACKUP/qualifiers input-specifier/qualifiers output-specifier/qualifiers

Table 10-2 lists the types of BACKUP command qualifiers.

Table 10-2 BACKUP Command Qualifier Types

Type	Position	Effect
Command qualifier	Anywhere on the command line	Affects both input and output specifiers.
Input specifier qualifier	Directly after the input specifier	Affects only the input specifier.
Output specifier qualifier	Directly after the output specifier	Affects only the output specifiers.

When you use BACKUP, make sure you place BACKUP qualifiers in their correct positions on the command line. For more information about the BACKUP command line, refer to the OpenVMS System Management Utilities Reference Manual.

10.4.1.1 Using Extended Character Sets

Beginning with OpenVMS Version 7.2, which introduces Extended File Specifications, BACKUP can process file names that have extended character sets. Included are the following formats:

• ODS-2 standard file name
• ISO Latin-1
• Unicode (UCS-2)

For additional information about extended character sets, refer to the OpenVMS Guide to Extended File Specifications.

10.4.1.2 Specifying Input Files

For file-based BACKUP operations, you can specify relative input file versions, for example:

$ BACKUP FILE.DAT;-2 SAVED_FILE.DAT

This example shows that you can choose the second-from-the-most-recent version of the input file and assign it a different file name.

With BACKUP, you cannot use -0 as a relative file version to specify the earliest version of the file. BACKUP processes -0 as if it were 0, saving the most recent version of the file for processing.

10.4.2 The Backup Manager

Backup Manager is a screen-oriented interface to the OpenVMS Backup utility (BACKUP) that presents BACKUP's capabilities in an intuitive, task-oriented, self-documenting manner. Backup Manager can ease backup tasks by guiding you through the backup process. No real performance differences exist between using the Backup Manager and using the BACKUP command line.

Backup Manager runs on:

• Any Compaq VTxxx-series video display terminal or equivalent terminal emulator
• VMS VAX Version 5.4 or higher systems, and OpenVMS Alpha Version 1.5 or higher systems

The Backup Manager interface is based on the OpenVMS Screen Management Run-Time Library (RTL) routines.

10.4.2.1 Backup Manager Features

Backup Manager can perform the following backup operations:

• Save an entire volume to a save set
• Save selected files from a volume to a save set
• Restore an entire volume from a save set
• Restore selected files from a save set
• List a save set

Three types of online assistance are available with Backup Manager:

• Context-sensitive help
  Press PF2 or the Help key to get help about the object at which the display cursor is currently located.
• Context-sensitive hints
  You are prompted for input by a one-line "hint" about the field where the display cursor is currently located.
• Pull-down help
  Choose the pull-down Help menu bar item for more extensive help on a variety of Backup Manager topics.

To start Backup Manager, enter the following command at the DCL prompt:

$ RUN SYS$SYSTEM:BACKUP$MANAGER

Output from the Backup utility is automatically displayed when an operation starts. You can suspend output at any time (Ctrl/P) and scroll through it. You can also use Ctrl/T to display status or Ctrl/C to stop the current BACKUP operation.

10.5 Understanding Save Sets

When you enter a BACKUP command to save files to a tape, BACKUP writes the files to a special file called a save set. You can also create a save set on a disk using the /SAVE_SET qualifier. Save sets are classified according to the media on which they reside. Table 10-3 lists the types of media that you write a save set to.

Table 10-3 Save-Set Types

Media Type	For More Information
Magnetic tape	Section 10.5.1
Files--11 disk	Section 10.5.2
Files--11 disk on a remote node (network save set)	Section 10.5.3
Sequential disk	Section 10.5.4

10.5.1 Magnetic Tape Save Sets

Magnetic tape is the most commonly used media for storing BACKUP save sets. It is less expensive than disk media, and its compact size makes it easy to store. You can use more than one tape device at a time to save or restore data; this allows processing to continue on another tape while the one most recently used is rewinding.

BACKUP treats all magnetic tape files as BACKUP save sets. Because you cannot use save-set specifications as both the input and output specifiers in a BACKUP command line, you cannot perform a BACKUP operation from one magnetic tape to another.

Compaq recommends that you copy magnetic tape save sets to disk with the BACKUP command; however, you can use the DCL command COPY on magnetic tape save sets that were created with the /INTERCHANGE qualifier.

Save-set specifications on magnetic tape are limited to 17 characters, including the period delimiter (.) and file type. The following text is a valid save-set specification:

WKLY27JAN1998.BCK

When restoring data from tape, if you do not include a save-set name with an input magnetic tape, BACKUP reads the next save set it encounters on the tape. (If you specify the input save-set qualifier /REWIND, BACKUP rewinds the tape and reads the first save set on the tape.)

10.5.2 Files--11 Disk Save Sets

To write save sets on a Files--11 disk, you must include the output save-set qualifier /SAVE_SET. The /SAVE_SET qualifier indicates to BACKUP that you want to create a save set, rather than a copy of the selected files, on the output volume. The disk must be mounted as a Files--11 volume; all volumes in a volume set must be mounted.

BACKUP can read a Files--11 save set as a Files--11 save set or as a sequential-disk save set:

• When BACKUP reads a save set as a Files--11 save set, all volumes of the save set must be mounted. To read a save set that is not located in your process default directory, you must specify the directory in which the save set is located.
• When BACKUP reads a Files--11 save set as a sequential-disk save set, you can mount the volumes one at a time. You must specify the master file directory [000000] in the save-set specification when reading a Files--11 save set as a sequential-disk save set.

A save set stored on a Files--11 disk is a standard file, however, and can be copied, renamed, deleted, or backed up.

10.5.3 Network Save Sets

You can create or read a network save set on a Files--11 disk attached to a remote node by specifying the node name of a remote node in the save-set specification. A remote node is accessible to the node you are working on (the host node) over a network. The network save set must be located on a publicly accessible disk (a disk mounted from the remote node with the /SYSTEM, /GROUP, or /CLUSTER qualifier) on the remote node.

Depending on the volume and file protection at the remote node, you may need to specify an access control string in the network save-set specification. An access control string includes the user name and password, and has the following format:

remote_nodename"username password"::device_name:[directory]

Example

The following example creates a network save set on the remote node DOUBLE:

$ BACKUP _FROM: [MY_DIR] _TO: DOUBLE"username password"::DBA0:SAVEIT.BCK/SAVE_SET

Omit the access control string if it is not required to gain access to the remote node, such as in the case of proxy network access. Refer to the DECnet for OpenVMS Networking Manual for more information about access control strings and proxy network access.

10.5.4 Sequential-Disk Save Sets

Sequential-disk save sets allow you to treat a Files--11 disk volume sequentially, (like a magnetic tape volume). The primary advantage of using sequential-disk save sets is that you can mount multivolume save sets one volume at a time. This is particularly useful on systems without tape drives that have a large fixed-media disk and a small removable disk.

When one sequential disk is full, BACKUP prompts you to mount another disk. You can use more than one disk device at a time to save or restore data; this allows processing to continue on another disk while the one most recently used is spinning down.

You must have the privilege LOG_IO or PHY_IO to read or write a multivolume sequential-disk save set.

Before creating a sequential-disk save set, mount the first volume of the sequential-disk save set using the DCL command MOUNT/FOREIGN. Although the disk is mounted with the /FOREIGN qualifier, BACKUP manages the disk using Files--11 structure.

When you perform a save operation to a sequential disk, you must use the output save-set qualifier /SAVE_SET. When you perform a restore operation from a sequential disk, you must specify the input save-set qualifier /SAVE_SET. If you do not specify the /SAVE_SET qualifier, BACKUP displays the following error message:

%BACKUP-F-IMGFILSPE, /IMAGE specification must only have device name

Do not specify a directory name for the save set; sequential-disk save sets are always entered in the master file directory [000000]. Even if you specify a directory other than the master file directory in a save operation, the save set is entered in the master file directory. If you specify a directory other than the master file directory in a restore or list operation, BACKUP returns an error message indicating that it cannot locate the file.

BACKUP does not initialize the first sequential-disk volume because the default is /NOINITIALIZE; however, continuation volumes are initialized. Unless you specify the command qualifier /INITIALIZE, the following restrictions apply to the first sequential-disk volume:

• The disk must be Files--11 Structure Level 2 or 5.
• The disk must not be part of a volume set.
• The cluster factor of the disk must be 1.
• The free space on the disk cannot be fragmented into more than 100 contiguous extents.
• The index file cannot be extended.
• The master file directory cannot be extended.

Volumes you use for sequential-disk save sets should contain only save sets. You must initialize a volume that has been used for general file processing before using it as a sequential-disk volume. You can place a maximum of 12 save sets on a single sequential disk. Use Files--11 disk save sets if you want to create more than 12 save sets on a single disk.

BACKUP can read a sequential-disk save set either as a sequential-disk save set or as a Files--11 save set:

• When BACKUP reads a save set as a sequential-disk save set, the save set can be mounted one volume at a time. The default directory for the save set file specification is the master file directory [000000] on the disk.
• When BACKUP reads a save set as a Files--11 save set, all volumes of the save set must be mounted. The default directory is your process default directory. Therefore, you must specify the master file directory [000000] in order to read a sequential-disk save set as a Files--11 save set.

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