You should think ofa shadow set as a single, highly available disk. As such, backuptechniques for nonshadowed disks apply to shadow set virtual units.However, to preserve the consistency and integrity of the shadowset, avoid removing a physical member of the shadow set withoutdismounting the virtual unit unless you have scrupulously followedthe guidelines in Guidelines for Using a Shadow Set Member for Backup. If you leave some disk members of a shadowset active during the backup operation, data integrity is compromisedbecause some disks in the shadow set may have files open. Referto Dismounting and Remounting With One Less Member for Backup forinformation about obtaining a member of a shadow set for the sourceof a backup operation.
The following list describes options that are available whenbacking up shadow sets that are not available with nonshadowed disks.
To obtain a defragmented backup ofa shadowed disk, begin by closing files and stopping application accessto the disks. Dismount the virtual unit to dissolve the shadow set.Use the /NOUNLOAD qualifier to avoid spinning down the members ofthe shadow set. Remount the virtual unit as a private device, and useBACKUP/IMAGE (see Using BACKUP/IMAGE on a Shadow Set)with the virtual unit as the source of the backup operation. Thisis the recommended method of backing up shadow sets.
To minimize the amount of time that data is unavailableto applications, consider remounting the shadow set with one lessmember (see Dismounting and Remounting With One Less Member for Backup). Then back up the dismounted member. This technique keepsthe shadow set in service at the same time that you perform a backupoperation. Once the backup is complete, remount the member into theshadow set. The shadowing software performs a copy, or minicopy,operation to make that member consistent with the other membersof the shadow set. If a spare disk of the type present in the shadow set is available,consider mounting the spare disk into the shadow set to minimizethe time that the shadow set runs with reduced membership. Then,the member that served as the source of the backup can become aspare disk.
To ensure complete integrity of the backup of thesystem disk, you must shut down the systems that boot from it. Forsystem disk shadow sets, you should also dismount the virtual unitby any other systems that have it mounted. Then remount the virtualunit as a private device on one of the systems that was not shutdown, and use it as the source for a BACKUP/IMAGE operations (see Using BACKUP/IMAGE on a Shadow Set). In addition, to provide system disk shadowing quickly as youperform a backup operation, remount the shadow set minus one member.Back up that member and either remount it into the shadow set ormount a spare disk. You can use standalone BACKUP (VAX) or the menu-drivenBACKUP procedure (Alpha) on one of the systems that is down whilethe other systems are rebooted.
To do an incremental backup, use the virtual unit,not a single member of the shadow set. This is because incrementalbackups alter information in file headers. If you perform an incrementalbackup on a removed member of a shadow set, that member needs tobe the target of a copy operation.
HSC BACKUP and RESTORE techniques are not recommended forsaving and restoring the contents of a shadow set member. TheseHSC utilities are applicable to the disk geometry only, not to theOpenVMS file system. Although HSC BACKUP and RESTORE techniquessave and restore the contents of an entire disk volume (includingblocks 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 defragmenta disk. Moreover, the utilities cannot restore the context of ashadow set virtual unit.
The following sections describe several approaches to shadowset backup operations.
Restrictions on BACKUP Procedures On VAX systems, accessing shadow sets from standalone BACKUPis not supported. The command procedures supplied with OpenVMS forbuilding standalone BACKUP kits are designed to prevent standaloneBACKUP from using volume shadowing improperly. However, these checkscan easily be overridden by a well-informed and sufficiently privilegeduser.
Note the following restrictions for standalone BACKUP on VAXsystems that use volume shadowing:
Do not boot standalone BACKUP froman alternative root on a shadowed system disk while other nodes arebooting from the same shadowed system disk. If you do this, theboot attempt will fail.
Standalone BACKUP does not mount virtual units.This makes access to virtual units impossible from standalone BACKUP.
Do not assume that standalone BACKUP prevents youfrom accessing a shadow set member unit. You must prevent standaloneBACKUP from sending output to a disk mounted on any other OpenVMS Clustermember, either as a directly accessible disk or as the member ofa shadow set.
On Alpha computers, the same restrictions apply. You cannotuse the standalone, menu-driven procedure included on the OpenVMSAlpha operating system distribution compact disc to perform BACKUPoperations on shadow sets.
Using Copy Operations to Create a Backup This example showshow to use volume shadowing copy operations to create an offlineidentical disk volume that you can then use as a backup of yourshadow set. The following command creates a shadow set with one shadowset 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 theshadow 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 completebefore dismounting the shadow set. When the copy operation is complete,messages are sent to the system console and to any operators enabledto receive them.
The following command dismounts the shadow set, leaving $1$DUA10and $1$DUA11 with logically identical volumes:
$ DISMOUNT DSA0:
At this point you can re-create the shadow set with one ofthe volumes and keep the other as a backup, or use it as a sourcefor the backup operation.
Using the OpenVMS Backup Utility Generallyyou can use the OpenVMS Backup utility (BACKUP) with shadow setsas you do with regular volumes. (See the HP OpenVMS System Manager'sManual for a description of how to back up volumes.) You can createBACKUP save sets or copies from shadow sets by using the shadowset virtual unit name instead of a physical device name as the inputspecifier. However, you cannot always restore to a shadow set by listingthe virtual unit name as an output specifier. The main restrictionto any backup restoration is that you cannot mount the target volumewith the /FOREIGN qualifier. The proper procedure for a BACKUP/IMAGE restorationis 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 followingcommand, for example, designates a virtual unit for the input specifier:
This command saves all files on the shadow set DSA2 that havebeen created or modified since the last backup and records the currenttime as their new backup date.
Using BACKUP/IMAGE on a Shadow Set You must take special precautions when you restore a shadowset from a BACKUP/IMAGE save set. (See the HP OpenVMS System Manager'sManual and the HP OpenVMS System Management Utilities Reference Manual fora description of BACKUP/IMAGE operations with physical volumes.)A BACKUP/IMAGE operation marks the target volume as more currentthan the other shadow set members. This designates it as the sourceof copy operations if you re-create the shadow set with it.
Although you can create BACKUP save sets or copies from shadowset virtual units, you cannot mount your shadow set with the /FOREIGNqualifier to allow a BACKUP/IMAGE restoration.
You should either restore to a physical disk and then re-createthe shadow set with the restored disk as a shadow set member (Example2) or, if the save operation was a copy to a compatible disk, re-createthe shadow set with that disk as a member (Example 3). The targetof the BACKUP/IMAGE operation becomes the source of copy operationsif you re-create the shadow set with it.
Example 1
This example shows how to perform a backup on a former shadowset 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 sureall copy operations are finished before you dismount the shadowset 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 online.
$ 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 anda magnetic tape in preparation for a BACKUP command.
$ BACKUP/IMAGE $1$DUA11: MTA0:SAVESET.BCK
This command produces a BACKUP/IMAGE save set from $1$DUA11while the shadow set is on line with $1$DUA10.
Example 2
This example shows how to restore a shadow set from an imagesave set. Restoring an image save set directly toa shadow set is not supported because the BACKUP output medium (theshadow set) must be mounted as a foreign volume.
These two commands mount the save-set magnetic tape as theinput specifier and the former shadow set member as the output specifierfor 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 preparationfor mounting into a shadow set.
Do not attempt to add the restored volume to an existingshadow set without first dissolving the original shadow set. Mountinga restored volume into an existing shadow set will result in a copyoperation 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 shadowset member. The output of the image backup operation has a newergeneration number than other previous members of the shadow set.Therefore, $1$DUA10 (the restored volume) is the source of a copyoperation when you form the shadow set.
Example 3
This example illustrates a BACKUP/IMAGE copy operation ona shadow set. The image backup operation stores output files contiguously,eliminating disk fragmentation. Because you must mount the outputdevice of such operations with the /FOREIGN qualifier, you musttake 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 commandmounts, on $1$DUA20, the volume to be the output of the BACKUP/IMAGEoperation. The /FOREIGN qualifier is required.
$ BACKUP/IMAGE/IGNORE=INTERLOCK DSA0: $1$DUA20:
This command performs the image backup using the virtual unitname as the input specifier. The image backup copy of a shadow sethas a newer backup revision number than the existing members inthe shadow set.
If any writes occur between the start of the backupoperation and the dismount of both the volume containing the imagebackup copy and the shadow set, the backup image will not containall the data on the shadow set. You can prevent any writes fromoccurring during this period by mounting the shadow set with the/NOWRITE qualifier prior to mounting the volume that will serveas the backup volume.
$ DISMOUNT $1$DUA20: $ DISMOUNT DSA0:
These commands dismount the target of the image backup andthe 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 backupdisk as one of the shadow set members. The other former shadow setmembers receive copy operations.
HP Volume Shadowing for OpenVMS
Performing System Management Tasks on Shadowed... 
