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.
See “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.
To obtain a defragmented
backup of a shadowed disk, begin by closing files and stopping application
access to the disks. Dismount the virtual unit to dissolve the shadow
set. Use the /NOUNLOAD qualifier to avoid spinning down the members
of the shadow set. Remount the virtual unit as a private device, and
use BACKUP/IMAGE (see “Using BACKUP/IMAGE on a Shadow Set”) with the virtual unit as the source of the
backup operation. This is the recommended method of backing up shadow
sets.
To minimize the amount
of time that data is unavailable to applications, consider remounting
the shadow set with one less member (see “Dismounting and Remounting With One Less Member for Backup”). Then
back up the dismounted member. This technique keeps the shadow set
in service at the same time that you perform a backup operation. Once
the backup is complete, remount the member into the shadow set. The
shadowing software performs a copy, or minicopy, operation to make
that member consistent with the other members of 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 minimize the time that the shadow set runs with reduced membership.
Then, the member that served as the source of the backup can become
a spare disk.
To ensure complete integrity
of the backup of the system disk, you must shut down the systems that
boot from it. For system disk shadow sets, you should also dismount
the virtual unit by any other systems that have it mounted. Then remount
the virtual unit as a private device on one of the systems that was
not shut down, 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 you perform a backup operation, remount the shadow set
minus one member. Back up that member and either remount it into the
shadow set or mount a spare disk. You can use
the menu-driven BACKUP procedure on one of the systems
that is down while the other systems are rebooted.
To do an incremental backup,
use the virtual unit, not a single member of the shadow set. This
is because incremental backups alter information in file headers.
If you perform an incremental backup on a removed member of a shadow
set, that member needs to be the target of a copy operation.
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 |
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On Alpha computers, 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.
Note the following restrictions for standalone
BACKUP that use volume shadowing:
Do not boot standalone
BACKUP from an alternative root on a shadowed system disk while other
nodes are booting from the same shadowed system disk. If you do this,
the boot attempt fails.
Standalone BACKUP does
not mount virtual units. This makes access to virtual units impossible
from standalone BACKUP.
Do not assume that standalone
BACKUP prevents you from accessing a shadow set member unit. You must
prevent standalone BACKUP from sending output to a disk mounted on
any other OpenVMS Cluster member, either as a directly accessible
disk or as the member of a shadow set.
Using Copy Operations to Create a Backup |
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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:
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 |
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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 |
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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:
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.
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| |
|
 | NOTE: Do 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 results in
a copy operation erasing the restored disk. |
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| |
|
$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.
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| NOTE: If 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 does 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 serves as the backup volume. |
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| |
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$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.
