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Performing Backup Operations on a Shadow Set  



You should think of a shadow set as a single, highly available disk. As such, backup techniques for nonshadowed disks apply to shadow set virtual units. However, to preserve the consistency and integrity of the shadow set, avoid removing a physical member of the shadow set without dismounting the virtual unit unless you have scrupulously followed the guidelines in Guidelines for Using a Shadow Set Member for Backup. If you leave some disk members of a shadow set active during the backup operation, data integrity is compromised because some disks in the shadow set may have files open. Refer to Dismounting and Remounting With One Less Member for Backup for information about obtaining a member of a shadow set for the source of a backup operation.

The following list describes options that are available when backing up shadow sets that are not available with nonshadowed disks.

HSC BACKUP and RESTORE techniques are not recommended for saving and restoring the contents of a shadow set member. These HSC utilities are applicable to the disk geometry only, not to the OpenVMS file system. Although HSC BACKUP and RESTORE techniques save and restore the contents of an entire disk volume (including blocks that may not be in use by the file system on that volume), they do not save and restore specific files, groups of files, directories, or subdirectories. In addition, these utilities do not defragment a disk. Moreover, the utilities cannot restore the context of a shadow set virtual unit.

The following sections describe several approaches to shadow set backup operations.

Restrictions on BACKUP Procedures  

On VAX systems, accessing shadow sets from standalone BACKUP is not supported. The command procedures supplied with OpenVMS for building standalone BACKUP kits are designed to prevent standalone BACKUP from using volume shadowing improperly. However, these checks can easily be overridden by a well-informed and sufficiently privileged user.

Note the following restrictions for standalone BACKUP on VAX systems that use volume shadowing:

On Alpha computers, the same restrictions apply. You cannot use the standalone, menu-driven procedure included on the OpenVMS Alpha operating system distribution compact disc to perform BACKUP operations on shadow sets.

Using Copy Operations to Create a Backup  

This example shows how to use volume shadowing copy operations to create an offline identical disk volume that you can then use as a backup of your shadow set. The following command creates a shadow set with one shadow set member:

MOUNT DSA0:/SHADOW=$1$DUA10: SHADOWFACTS
%MOUNT-I-MOUNTED, SHADOWFACTS  mounted on _DSA0: 
%MOUNT-I-SHDWMEMSUCC, _$1$DUA10: (DISK01) is now a 
                      valid member of the shadow set


The following command adds a second member, $1$DUA11, to the shadow set:

MOUNT DSA0:/SHADOW=$1$DUA11: SHADOWFACTS
%MOUNT-I-SHDWMEMCOPY, _$1$DUA11: (DISK02) added to the shadow 
                      set with a copy operation


At this point you must wait for the copy operation to complete before dismounting the shadow set. When the copy operation is complete, messages are sent to the system console and to any operators enabled to receive them.

The following command dismounts the shadow set, leaving $1$DUA10 and $1$DUA11 with logically identical volumes:

$ DISMOUNT DSA0:


At this point you can re-create the shadow set with one of the volumes and keep the other as a backup, or use it as a source for the backup operation.

Using the OpenVMS Backup Utility   

Generally you can use the OpenVMS Backup utility (BACKUP) with shadow sets as you do with regular volumes. (See the HP OpenVMS System Manager's Manual for a description of how to back up volumes.) You can create BACKUP save sets or copies from shadow sets by using the shadow set virtual unit name instead of a physical device name as the input specifier. However, you cannot always restore to a shadow set by listing the virtual unit name as an output specifier. The main restriction to any backup restoration is that you cannot mount the target volume with the /FOREIGN qualifier. The proper procedure for a BACKUP/IMAGE restoration is described in Using BACKUP/IMAGE on a Shadow Set.

The format for a BACKUP command is as follows: BACKUP input-specifier output-specifier

The format is the same as for any BACKUP operation. The following command, for example, designates a virtual unit for the input specifier:

$ BACKUP/RECORD DSA2:[*...]/SINCE=BACKUP MTA0:23DEC.BCK


$ BACKUP/RECORD DSA2:[*...]/SINCE=BACKUP MTA0:23DEC.BCK


This command saves all files on the shadow set DSA2 that have been created or modified since the last backup and records the current time as their new backup date.

Using BACKUP/IMAGE on a Shadow Set  

You must take special precautions when you restore a shadow set from a BACKUP/IMAGE save set. (See the HP OpenVMS System Manager's Manual and the HP OpenVMS System Management Utilities Reference Manual for a description of BACKUP/IMAGE operations with physical volumes.) A BACKUP/IMAGE operation marks the target volume as more current than the other shadow set members. This designates it as the source of copy operations if you re-create the shadow set with it.

Although you can create BACKUP save sets or copies from shadow set virtual units, you cannot mount your shadow set with the /FOREIGN qualifier to allow a BACKUP/IMAGE restoration.

You should either restore to a physical disk and then re-create the shadow set with the restored disk as a shadow set member (Example 2) or, if the save operation was a copy to a compatible disk, re-create the shadow set with that disk as a member (Example 3). The target of the BACKUP/IMAGE operation becomes the source of copy operations if you re-create the shadow set with it.

Example 1

This example shows how to perform a backup on a former shadow set member after you rebuild the shadow set.

MOUNT DSA0:/SHADOW=($1$DUA10:, $1$DUA11:)  GHOSTVOL
%MOUNT-I-MOUNTED, GHOSTVOL     mounted on _DSA0: 
%MOUNT-I-SHDWMEMSUCC, _$1$DUA10: (DISK01) is now a valid 
                      member of the shadow set
%MOUNT-I-SHDWMEMSUCC, _$1$DUA11: (DISK02) is now a valid 
                      member of the shadow set


The previous command mounts the shadow set DSA0. Make sure all copy operations are finished before you dismount the shadow set by using the following command:

$ DISMOUNT DSA0:


This command dismounts the shadow set.

MOUNT/SYSTEM DSA0/SHADOW=$1$DUA10: GHOSTVOL
%MOUNT-I-MOUNTED, GHOSTVOL    mounted on _DSA0: 
%MOUNT-I-SHDWMEMSUCC, _$1$DUA10: (DISK01) is now a valid 
                      member of the shadow set


This command puts the shadow set back on line without $1$DUA11. You can now perform the backup to tape while the shadow set is on line.

MOUNT $1$DUA11: GHOSTVOL
%MOUNT-W-VOLSHDWMEM, mounting a shadow set member volume 
                     volume write locked
%MOUNT-I-MOUNTED, GHOSTVOL mounted on _$1$DUA11: 

MOUNT/FOREIGN  MTA0:
%MOUNT-I-MOUNTED, ...


These two commands mount the former shadow set member and a magnetic tape in preparation for a BACKUP command.

$ BACKUP/IMAGE $1$DUA11: MTA0:SAVESET.BCK


This command produces a BACKUP/IMAGE save set from $1$DUA11 while the shadow set is on line with $1$DUA10.

Example 2

This example shows how to restore a shadow set from an image save set. Restoring an image save set directly to a shadow set is not supported because the BACKUP output medium (the shadow set) must be mounted as a foreign volume.

DISMOUNT DSA0:
MOUNT/FOREIGN MTA0:
%MOUNT-I-MOUNTED, ... 


MOUNT/FOREIGN/OVERRIDE=SHADOW_MEMBERSHIP $1$DUA10:
%MOUNT-I-MOUNTED, ... 


These two commands mount the save-set magnetic tape as the input specifier and the former shadow set member as the output specifier for the restore operation.

$ BACKUP/IMAGE MTA0:SAVESET.BCK $1$DUA10:


This command restores $1$DUA10 from the save set.

$ DISMOUNT/NOUNLOAD $1$DUA10:


This command dismounts the restored volume in preparation for mounting into a shadow set.


NoteDo not attempt to add the restored volume to an existing shadow set without first dissolving the original shadow set. Mounting a restored volume into an existing shadow set will result in a copy operation erasing the restored disk.



MOUNT/SYSTEM DSA0/SHADOW=($1$DUA10:, $1$DUA11:) GHOSTVOL
%MOUNT-I-MOUNTED, GHOSTVOL    mounted on _DSA0: 
%MOUNT-I-SHDWMEMSUCC, _$1$DUA10: (DISK01) is now a valid member of
                      the shadow set
%MOUNT-I-SHDWMEMCOPY, _$1$DUA11: (DISK02) added to the shadow set
                      with a copy operation


This command mounts the shadow set with the restored shadow set member. The output of the image backup operation has a newer generation number than other previous members of the shadow set. Therefore, $1$DUA10 (the restored volume) is the source of a copy operation when you form the shadow set.

Example 3

This example illustrates a BACKUP/IMAGE copy operation on a shadow set. The image backup operation stores output files contiguously, eliminating disk fragmentation. Because you must mount the output device of such operations with the /FOREIGN qualifier, you must take special steps as shown with the following commands:

MOUNT DSA0:/SHADOW=($1$DUA10:,$1$DUA11:)  MEANDMY
%MOUNT-I-MOUNTED, MEANDMY     mounted on _DSA0: 
%MOUNT-I-SHDWMEMSUCC, _$1$DUA10: (DISK03) is now a valid 
                      member of the shadow set
%MOUNT-I-SHDWMEMSUCC, _$1$DUA11: (DISK04) is now a valid 
                      member of the shadow set
MOUNT/FOREIGN $1$DUA20:
%MOUNT-I-MOUNTED, ... 


The first command mounts the shadow set DSA0. The second command mounts, on $1$DUA20, the volume to be the output of the BACKUP/IMAGE operation. The /FOREIGN qualifier is required.

$ BACKUP/IMAGE/IGNORE=INTERLOCK DSA0: $1$DUA20:


This command performs the image backup using the virtual unit name as the input specifier. The image backup copy of a shadow set has a newer backup revision number than the existing members in the shadow set.


NoteIf any writes occur between the start of the backup operation and the dismount of both the volume containing the image backup copy and the shadow set, the backup image will not contain all the data on the shadow set. You can prevent any writes from occurring during this period by mounting the shadow set with the /NOWRITE qualifier prior to mounting the volume that will serve as the backup volume.



DISMOUNT $1$DUA20:
DISMOUNT DSA0:


These commands dismount the target of the image backup and the shadow set, in preparation for re-creating the shadow set.

MOUNT/SYSTEM DSA0/SHADOW=($1$DUA10:,$1$DUA11:,$1$DUA20:) MEANDMY
%MOUNT-I-MOUNTED, MEANDMY     mounted on _DSA0: 
%MOUNT-I-SHDWMEMSUCC, _$1$DUA20: (DISK05) is now a valid 
                      member of the shadow set
%MOUNT-I-SHDWMEMCOPY, _$1$DUA10: (DISK03) added to the shadow 
                      set with a copy operation
%MOUNT-I-SHDWMEMCOPY, _$1$DUA11: (DISK04) added to the shadow 
                      set with a copy operation


This command rebuilds the shadow set with the image backup disk as one of the shadow set members. The other former shadow set members receive copy operations.
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