|Document revision date: 30 March 2001|
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:
|Formulating a BACKUP strategy||Section 11.3|
|Setting process quotas for efficient backups||Section 11.7|
|Using disks and tapes||Section 11.8|
|Listing the contents of a BACKUP save set||Section 11.10|
|Backing up user disks and volume shadow sets||Section 11.15|
|Restoring user disks and volume shadow sets||Section 11.16|
|Backing up and restoring the system disk||Section 11.17|
|Ensuring data integrity||Section 11.18|
This chapter explains the following concepts:
|Types of backups||Section 11.2|
|The BACKUP command line||Section 11.4.1|
|The Backup Manager||Section 11.4.2|
|Save sets||Section 11.5|
|BACKUP file formats||Section 11.6|
|Volume initialization||Section 11.8.1|
|OPCOM and volumes||Section 11.9|
|Multivolume BACKUP operations||Section 11.11|
|BACKUP tape label processing||Section 11.12|
|Standalone BACKUP (VAX only)||Section 11.17.2|
See Guidelines for OpenVMS Cluster Configurations for information about using BACKUP when your backup
medium is connected to a Fibre Channel interconnect.
11.1 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:
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.
Some layered products have their own special backup procedures. For more information, refer to the layered product documentation.
11.2 Understanding Types of Backups
The following table lists the types of backup operations.
|File operation||Processes individual files or directories. Section 11.13 describes file operations.|
Processes files or volumes selectively, according to criteria such as
version number, file type, UIC, date and time of creation, expiration
date, or modification date.
Performs selective save operations by using wildcard characters and input file-selection qualifiers (for example, /BACKUP, /BEFORE, /BY_OWNER [/OWNER_UIC], /CREATED, /EXCLUDE, /EXPIRED, /MODIFIED, and /SINCE). Section 11.13 describes selective operations.
|Physical operation||Copies, saves, restores, or compares an entire volume in terms of logical blocks, ignoring any file structure.|
Processes all files on the input disk. The types of image operations
Because an image copy or backup operation processes all files on the input volume, you cannot specify file-selection qualifiers for these operations. You can, however, restore files and directories selectively from an image save set.
The two types of incremental operations are:
Two types of BACKUP operations, file and image, support converting ODS-5 file names to ODS-2 file names. Refer to Section 22.214.171.124 for more information.
11.3 Formulating a Backup Strategy
When formulating a backup strategy, keep in mind the specific
requirements of your site and the advantages and disadvantages of the
different types of backups. Your backup strategy also depends on the
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 11-1 compares image and incremental backups.
|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 11.15.1).|
|Incremental||Takes less time and media storage space.||More difficult to restore files. Still requires periodic image backups.|
Before you perform an image backup, note the following items:
You do not have to change tapes or disks during a backup if any of the following statements is true:
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 11.15.7 contains some sample
command procedures that you can run in a batch job to back up your
11.4 Understanding the Backup Interfaces
Two interfaces are available to the OpenVMS Backup utility:
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 11-2 lists the types of BACKUP command qualifiers.
|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.
126.96.36.199 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:
For additional information about extended character sets, refer to the
OpenVMS Guide to Extended File Specifications.
188.8.131.52 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.
11.4.2 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:
The Backup Manager interface is based on the OpenVMS Screen Management
Run-Time Library (RTL) routines.
184.108.40.206 Backup Manager Features
Backup Manager can perform the following backup operations:
Three types of online assistance are available with Backup Manager:
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.
11.5 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 11-3 lists the types of media that you write a save set to.
|Media Type||For More Information|
|Magnetic tape||Section 11.5.1|
|Files--11 disk||Section 11.5.2|
|Files--11 disk on a remote node (network save set)||Section 11.5.3|
|Sequential disk||Section 11.5.4|
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:
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
11.5.2 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:
A save set stored on a Files--11 disk is a standard file, however, and
can be copied, renamed, deleted, or backed up.
11.5.3 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:
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.
11.5.4 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 . 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:
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:
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