HP OpenVMS Systems Documentation

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Volume Shadowing for OpenVMS

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7.12.12 Testing

Testing alone cannot guarantee the correctness of a backup procedure. However, testing is a critical component of designing any backup and recovery process.

7.12.13 Restoring Data

Too often, organizations concentrate on the backup process with little thought to how their data will be restored. Remember that the ultimate goal of any backup strategy is to recover data in the event of a disaster. Restore and recovery procedures must be designed and tested as carefully as the backup procedures.

7.12.14 Revalidation of Data Consistency Methods

The discussion in this section is based on features and behavior of OpenVMS Version 7.3 and applies to prior versions as well. Future versions of OpenVMS may have additional features or different behavior that affect the procedures necessary for data consistency. Sites that upgrade to future versions of OpenVMS must reevaluate their procedures and be prepared to make changes or to employ nonstandard settings in OpenVMS to ensure that their backups remain consistent.

Chapter 8
Performing System Management Tasks on Shadowed Systems

This chapter explains how to accomplish system maintenance tasks on a standalone system or an OpenVMS Cluster system that uses volume shadowing. Refer to Chapter 3 for information about setting up and booting a system to use volume shadowing.

8.1 Upgrading the Operating System on a System Disk Shadow Set

It is important to upgrade the operating system at a time when your system can afford to have its shadowing support disabled. This is because you cannot upgrade to new versions of the OpenVMS operating system on a shadowed system disk. If you attempt to upgrade a system disk while it is an active member of a shadow set, the upgrade procedure will fail.

Procedure for Upgrading Your Operating System

This procedure is divided into four parts. Part 1 describes how to prepare a shadowed system disk for the upgrade. Part 2 describes how to perform the upgrade. Part 3 describes how to enable volume shadowing on the upgraded system. Part 4 shows how to boot other nodes in an OpenVMS Cluster system with and without volume shadowing.

Part 1: Preparing a Shadowed System Disk

  1. On OpenVMS Cluster systems, choose the node on which you want to perform the upgrade.
  2. Create a nonshadowed system disk to do the upgrade using either of these methods:
    • Prepare a copy of the current system disk to use as the target of the upgrade procedure. See Section 8.3.2.
    • Use BACKUP to create a compressed copy of the shadow set on a single scratch disk (a disk with no useful data). See in Section 8.3.4 for an example.
  3. Enter the MOUNT/OVERRIDE=SHADOW_MEMBERSHIP command on the upgrade disk to zero the shadowing-specific information on the storage control block (SCB) of the disk. Do not mount the disk for systemwide or clusterwide access; omit the /SYSTEM and /CLUSTER qualifiers on the MOUNT command line.
  4. Use the DCL command SET VOLUME/LABEL=volume-label device-spec[:] to change the label on the upgrade disk. (The SET VOLUME/LABEL command requires write access [W] to the index file on the volume. If you are not the volume owner, you must have either a system UIC or the SYSPRV privilege.) For OpenVMS Cluster systems, ensure that the volume label is a unique name across the cluster.


    If you need to change the volume label of a disk that is mounted across the cluster, be sure you change the label on all nodes in the OpenVMS Cluster system. For example, you could propagate the volume label change to all nodes in the cluster with one SYSMAN utility command, after you define the environment as the cluster:

    SYSMAN> DO SET VOLUME/LABEL=new-label disk-device-name:
  5. Ensure that the boot command line or file boots from the upgrade disk. The manner in which you store the boot command information depends on the processor on which you are working. For more information about storing boot commands, see the instructions in your hardware installation guide, the upgrade and installation supplement for your VAX computer, or the upgrade and installation manual for your Alpha computer.
    If volume shadowing is enabled on the node, disable it according to the instructions in step 6. Otherwise, continue with Part 2 to upgrade the system.
  6. Prepare to perform the upgrade procedure by disabling system disk shadowing (if it is enabled) on the node to be upgraded.


    You cannot perform an upgrade on a shadowed system disk. If your system is set up to boot from a shadow set, you must disable shadowing the system disk before performing the upgrade. This requires changing SYSGEN parameter values interactively using the SYSGEN utility.

    Invoke SYSGEN by entering the following command:


    On OpenVMS Alpha systems, enter the following:


    On OpenVMS VAX systems, enter the following:

    The USE command defines the system parameter file from which data is to be retrieved. You should replace the variable upgrade-disk with the name of the disk to be upgraded. For the variable n in [SYSn.SYSEXE], use the system root directory you want to boot from (this is generally the same root you booted from before you started the upgrade procedure).
    Disable shadowing of the system disk by setting the SYSGEN parameter SHADOW_SYS_DISK to 0, as follows:


    On OpenVMS Alpha systems, enter:


    On OpenVMS VAX systems, enter:


    Type EXIT or press Ctrl/Z to exit the SYSGEN utility and return to the DCL command level.
    You must also change parameters in the MODPARAMS.DAT file before shutting down the system. Changing parameters before shutdown ensures that the new system parameter values take effect when AUTOGEN reads the MODPARAMS.DAT file and reboots the nodes. Edit upgrade-disk:[SYSn:SYSEXE]MODPARAMS.DAT and set SHADOWING and SHADOW_SYS_DISK to 0.

Even if you plan to use the upgraded system disk to upgrade the operating system on other OpenVMS Cluster nodes, you should complete the upgrade on one node before altering parameters for other nodes. Proceed to Part 2.

Part 2: Performing the Upgrade

  1. Boot from and perform the upgrade on the single, nonshadowed disk. Follow the upgrade procedure described in the OpenVMS upgrade and installation manual.
  2. If you are upgrading a system that already has the volume shadowing software installed and licensed, then skip to Part 3.
    Otherwise, you must register the Volume Shadowing for OpenVMS Product Authorization Key (PAK) or keys. PAK registration is described in the release notes and cover letter supplied with your installation kit.

Part 3: Enabling Volume Shadowing on the Upgraded System

Once the upgrade is complete and the upgraded node has finished running AUTOGEN, you can enable shadowing for the upgraded node using the following steps.

  1. Invoke the System Generation utility (SYSGEN) by entering the following command:


    The USE CURRENT command initializes the SYSGEN work area with the source information from the current system parameter file on disk. (To find out the current value of system parameters, use the SHOW command [for example, SHOW SHADOWING] to see the current system parameter values as well as the minimum, maximum, and default values of the parameters.)
    To enable shadowing, set the system parameter SHADOWING to 2. If the system disk is to be a shadow set, set the system parameter SHADOW_SYS_DISK to 1, and set the SHADOW_SYS_UNIT parameter to the unit number of the virtual unit, as follows (assume the system disk virtual unit is DSA54):


    Type EXIT or press Ctrl/Z to exit the SYSGEN utility and return to the DCL command level.
  2. To ensure that volume shadowing is enabled each time AUTOGEN executes, edit the SYS$SYSTEM:MODPARAMS.DAT file to set the shadowing parameters. For OpenVMS Cluster systems, set system parameters in MODPARAMS.DAT on each node that uses volume shadowing. See Chapter 3 for more information about editing the MODPARAMS.DAT file.
  3. Shut down the system on which you performed the upgrade, and reboot.

Part 4: Booting Other Nodes in the OpenVMS Cluster from the Upgraded Disk

If other nodes boot from the upgraded disk, the OpenVMS upgrade procedure automatically upgrades and runs AUTOGEN on each node when it is booted. The procedure for booting other nodes from the upgraded disk differs based on whether the upgraded disk has been made a shadow set.

  1. If the upgraded disk is not yet a shadow set:
    1. Disable shadowing (if it is enabled) for the system disk on the nodes to be upgraded.
    2. Alter the boot files for those nodes so they boot from the upgraded disk.
    3. Make sure the system parameters in the node-specific SYS$SYSTEM:MODPARAMS.DAT files are correct (as described in Section 3.3.1). When the OpenVMS upgrade procedure invokes AUTOGEN, it will use these parameter settings.
    4. Boot the nodes from the upgraded disk.
  2. If the upgraded disk is already a shadow set member, additional steps are required:
    1. For each node to be booted from the upgraded disk, edit VAXVMSSYS.PAR for VAX systems and ALPHAVMSSYS.PAR for Alpha systems, and MODPARAMS.DAT to enable system disk shadowing. Set SHADOWING to 2, SHADOW_SYS_DISK to 1, and SHADOW_SYS_UNIT to the number of the system disk's virtual unit name. Remember to modify the files on the upgraded disk, not on the system disk, prior to upgrade.
    2. Modify the computer console so that the system boots from the upgraded disk.
      On VAX computers, depending on which model you have, you can alter the boot file on the console media or use a console command to change nonvolatile RAM.
      On Alpha computers, you can use the SET BOOTDEF_DEV console command. For more information, see the hardware information or the upgrade and installation manual for your system.
    3. Boot each node. With shadowing enabled in each node's ALPHAVMSSYS.PAR or VAXVMSSYS.PAR on the upgraded disk, the node will be able to boot from the shadowed (upgraded) system disk.

Once you have successfully upgraded the system or systems and you have completed other postupgrade work (such as layered product installations), perform the following steps:

  1. Mount additional shadow set members into the shadow set, if necessary. Do not use a command procedure to add members to a system disk shadow set. For more information, see Section 3.4.
  2. Back up your new system disk shadow set. If you usually use online BACKUP for this task, you can use one of the procedures described in Section 8.3. If you usually use standalone BACKUP at this point, refer to Section 8.3.1.

8.2 Modifying Data on Individual Shadow Set Members

Generally, users and applications access a shadow set through the virtual unit. Occasionally, you may want to change the data on an individual shadow set member and then pass the changed data to other shadow set members.

The following series of commands demonstrates how you can dissolve and recreate the shadow set to perform specialized processes on one shadow set member and transfer the change to the other shadow set members.

The following command mounts a shadow set with three shadow set members:

$ MOUNT DSA9:/SHADOW=($45$DUA2:,$45$DUA4:,$45$DUA8:) LURK1

The following command dissolves the shadow set mounted in the previous command and makes the individual shadow set members available:


The following command mounts one former shadow set member as a disk volume outside of the shadow set:


In this command, in order to have write access, you must use the /OVERRIDE=SHADOW_MEMBERSHIP qualifier to zero the shadow set generation number. At this point, the disk is mounted as a nonshadowed volume and can be modified as required.

Before creating a new shadow set, dismount the $45$DUA2 physical disk, as follows:


The second command recreates the shadow set with $45$DUA2 as the only member.

Note that mounting $45$DUA2 with the /OVERRIDE=SHADOW_MEMBERSHIP qualifier automatically zeroed the volume shadowing generation number. If you were to specify all the former members of the shadow set in the same command line, the MOUNT command would consider $45$DUA2 an unrelated volume and would determine that it requires a copy operation. This would overwrite the earlier modifications.

To save the current contents of $45$DUA2, add the other two former shadow set members to the new shadow set with a subsequent MOUNT command:

$ MOUNT DSA9:/SHADOW=($45$DUA4:,$45$DUA8:) LURK1

In this command, $45$DUA4 and $45$DUA8 are added to the shadow set DSA9. This recreates the original shadow set, except that each shadow set member now has the benefit of the changed data that was done to the single shadow set member.

8.3 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 Section 7.12. 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 Section 4.8.3 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 Section 8.3.4) 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 Section 4.8.3). 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 Section 8.3.4).
    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 standalone BACKUP (VAX) or the menu-driven BACKUP procedure (Alpha) 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.

8.3.1 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:

  • 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 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 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.

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.

8.3.2 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-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-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.

8.3.3 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 OpenVMS System Manager's Manual, Volume 1: Essentials 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 Section 8.3.4.

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:



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.

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