Updated: 11 December 1998

Volume Shadowing for OpenVMS

To disable both the merge and copy performance assists on the HSC controller, follow these steps on each HSC controller for which you want to disable the assists:

1. Press Ctrl/C to get to the HSC prompt.
2. When the HSC> prompt appears on the terminal screen, enter the following commands:

   HSC> RUN SETSHO SETSHO> SET SERVER DISK/NOHOST_BASED_SHADOWING SETSHO-I Your settings require an IMMEDIATE reboot on exit. SETSHO> EXIT SETSHO-Q Rebooting HSC. Press RETURN to continue, CTRL/Y to abort:

After you issue these commands, the HSC controller automatically reboots:

INIPIO-I Booting...

To reenable the assists, follow the same procedure on your HSC controller, but use the /HOST_BASED_SHADOWING qualifier on the SET SERVER DISK command.

Use the HSC command SHOW ALL to see whether the assists are enabled or disabled. The following example shows a portion of the SHOW ALL display that indicates the shadowing assists status:

HSC> SHOW ALL . . . 2-Feb-1993 16:42:51.40 Boot: 5-Dec-1992 15:43:33.20 Up: 1416:59 Version: V650 System ID: %X00000000F906 Name: RDHSC6 Front Panel: Secure HSC Type: HSC70 Disk Server Options Enabled: Variant Protocol Host Based Shadowing Assists: Enabled Disk Drive Controller Timeout: 2 seconds Maximum Sectors per Track: 74 sectors Enhanced mode fragment size: 7 Enhanced mode DRAT buffers: 70 Reserved BMB count: 10 Disk Copy Data connection limit: 4 Active: 0 . . .

6.5 What Happens to a Shadow Set When a System Fails?

When a CPU, controller, or disk failure occurs, the shadowing software maintains data availability by performing the appropriate copy, merge, or minimerge operation. The effect on applications and users is minimal. The following subsections describe the courses of action taken when failures occur. The course of action taken depends on the event and whether the shadow set is in a steady state or a transient state.

Transitions from Steady State

When a shadow set is in a steady state, the following transitions can occur:

• If you mount a new disk into a steady state shadow set, the shadowing software performs a copy operation to make the new disk a full shadow set source member.
• If a failure occurs on a standalone system, the shadow set SCB reflects that the shadow set has been incorrectly dismounted. When the system is rebooted and the set remounted, a copy operation is not necessary but a merge operation is performed.
• If a failure occurs in a cluster, the shadow set is merged by a remaining node that has the shadow set mounted:
  • If performance assists are enabled, the shadowing software performs a minimerge.
  • If performance assists are not enabled, the shadowing software performs a merge operation.

Once the transition completes, the disks contain identical information and the shadow set returns to steady state.

Figure 6-1 illustrates these state transitions.

Figure 6-1 Steady State Transitions

Transitions During Copy Operations

The following list describes the transitions that can occur to a shadow set that is undergoing a copy operation:

• If you mount an additional disk into the shadow set that is already undergoing a copy operation, the shadowing software finishes the original copy operation before it begins another copy operation on the newly mounted disk.
• When a shadow set on a standalone system is undergoing a copy operation and the system fails, the copy operation aborts and the shadow set is left with the original members. For a standalone system, there is no recourse except to reboot the system and reinitiate the shadow set copy operation with a MOUNT command.
• When a shadow set in a cluster is undergoing a copy operation and the node performing the copy fails, another node in the cluster that has the shadow set mounted continues the copy operation automatically.

When a node failure occurs during a shadow set copy operation, merge behavior depends on whether or not the shadowing performance assists are enabled.

• If the minimerge is enabled, the shadowing software interrupts the copy operation to perform a minimerge and then resumes the copy operation.
• If the minimerge is not enabled, the shadowing software finishes the copy operation before beginning a merge operation.

Figure 6-2 illustrates these transitions.

Figure 6-2 Copy Operation Transitions

Transitions During Minimerge Operations

When a shadow set is undergoing a minimerge operation, the following transitions can occur:

• If a new member is mounted into a shadow set when a minimerge operation is in progress, the minimerge is completed before the copy operation is started.
• If another system failure occurs before the minimerge has completed, the action taken depends on whether or not the shadowing performance assists are enabled.
• If performance assists are enabled, the shadowing software restarts the minimerge from the beginning and adds new LBNs to the write log file based on the entries taken from the nodes that failed.
• If performance assists are disabled, the shadowing software reverts to a merge operation. The performance assists might be disabled if the controller runs out of write logs or if a failover occurs from a controller with write logs to one that does not.

Figure 6-3 illustrates these transitions.

Figure 6-3 Minimerge Operation Transitions

Transitions During Merge Operations

The following list describes the transitions that can occur to the shadow set that is undergoing a merge operation when performance assists are not available:

• If you add a new disk to a shadow set that is undergoing a merge operation, the shadowing software interrupts the merge operation to perform a copy operation. The merge operation resumes when the copy operation is completed.
• If a node failure occurs when the shadow set is performing a merge operation, the shadowing software abandons the current merge operation and starts a new merge operation.

Figure 6-4 illustrates these transitions.

Figure 6-4 Merge Operation Transitions

6.6 Examples of Copy and Merge Operations

In this example, DSA0 is the virtual unit name, $1$DUA8 and $1$DUA89 are the names of the disk volumes, and SHADOWDISK is the volume label.

Example 6-1 Copy Operation: Creating a New Shadow Set

$ MOUNT DSA0: /SHADOW=($1$DUA8:,$1$DUA89:) SHADOWDISK %MOUNT-I-MOUNTED, SHADOWDISK mounted on _DSA0: %MOUNT-I-SHDWMEMSUCC, _$1$DUA8: (FUSS) is now a valid member of the shadow set %MOUNT-I-SHDWMEMCOPY, _$1$DUA89: (FUSS) added to the shadow set with a copy operation $ SHOW DEVICES DSA0: Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA0: Mounted 0 SHADOWDISK 890937 1 1 $1$DUA8: (FUSS) ShadowSetMember 0 (member of DSA0:) $1$DUA89: (FUSS) ShadowCopying 0 (copy trgt DSA0: 1% copied)

The SHOW DEVICES display in Example 6-1 shows the shadow set during the copy operation (transient state). Because the SCB information on $1$DUA8 and $1$DUA89 indicates that these devices have never been part of a shadow set, the shadowing software uses the first device named in the command line ($1$DUA8) as the source of the copy operation. The device status "ShadowSetMember" indicates that the $1$DUA8 device is a source shadow set member, and "ShadowCopying" indicates that the physical device $11$DUA89 is the target of a copy operation.

Suppose you want to add a new member to an existing shadow set, and the device you add is a previous member of the shadow set. In this case, the volume label of the new member matches that of the current shadow set members, but the new member's MOUNT generation number is out of date compared with those of the current members. Thus, the Mount utility automatically performs a copy operation.

Example 6-2 shows the format of the MOUNT command and MOUNT status messages returned when you add the $3$DIA12 device to the shadow set represented by the DSA9999 virtual unit. Notice that you do not need to list the member units currently in the shadow set on the MOUNT command line.

Example 6-2 Copy Operation: Adding a Member to an Existing Shadow Set

$ MOUNT /SYSTEM DSA9999: /SHADOW=$3$DIA12: APPARITION %MOUNT-I-MOUNTED, APPARITION mounted on _DSA9999: %MOUNT-I-SHDWMEMCOPY, _$3$DIA12: (SHAD03) added to the shadow set with a copy operation $ SHOW DEVICES DSA9999: Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA9999: Mounted 0 APPARITION 70610 1 1 $3$DIA7: (BGFUSS) ShadowSetMember 0 (member of DSA9999:) $3$DIA5: (SHAD03) ShadowSetMember 0 (member of DSA9999:) $3$DIA12: (SHAD03) ShadowCopying 0 (copy trgt DSA9999: 87% copied)

Example 6-3 shows what happens if a three-member shadow set is dissolved on one node and then is immediately remounted on another node. When the Mount utility checks the volume information on each member, it finds that the volume information is consistent across the shadow set. Thus, a copy operation is not necessary when the shadow set is mounted.

In Example 6-3, DSA10 is the virtual unit and $3$DUA10, $3$DUA11, and $3$DUA12 are the member volumes. The first part of the example displays the output from a SHOW DEVICES command, which shows that the shadow set is mounted and in a steady state. Then the user dismounts the DSA10 shadow set and immediately remounts it.

Example 6-3 No Copy Operation: Rebuilding a Shadow Set

$ SHOW DEVICES D Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA10: Mounted 0 EIDOLON 292971 1 1 $3$DUA10: (MYNODE) ShadowSetMember 0 (member of DSA10:) $3$DUA11: (MYNODE) ShadowSetMember 0 (member of DSA10:) $3$DUA12: (MYNODE) ShadowSetMember 0 (member of DSA10:) $ DISMOUNT /NOUNLOAD DSA10: %%%%%%%%%%% OPCOM 24-MAR-1990 20:26:41.40 %%%%%%%%%%% $3$DUA10: (MYNODE) has been removed from shadow set. %%%%%%%%%%% OPCOM 24-MAR-1990 20:26:41.69 %%%%%%%%%%% $3$DUA11: (MYNODE) has been removed from shadow set. %%%%%%%%%%% OPCOM 24-MAR-1990 20:26:41.69 %%%%%%%%%%% $3$DUA12: (MYNODE) has been removed from shadow set. %%%%%%%%%%% OPCOM 24-MAR-1990 20:26:41.69 %%%%%%%%%%% $ MOUNT /SYSTEM DSA10: /SHADOW=($3$DUA10:, $3$DUA11:, $3$DUA12:) EIDOLON %MOUNT-I-MOUNTED, EIDOLON mounted on _DSA10: %MOUNT-I-SHDWMEMSUCC, _$3$DUA10: (MYNODE) is now a valid member of the shadow set %MOUNT-I-SHDWMEMSUCC, _$3$DUA11: (MYNODE) is now a valid member of the shadow set %MOUNT-I-SHDWMEMSUCC, _$3$DUA12: (MYNODE) is now a valid member of the shadow set $

Example 6-4 shows the output from the SHOW DEVICES command at the time of the merge operation.

When a system fails the volume information is left in a state that shows that the shadow set member was not dismounted. If you issue the MOUNT command again after the node reboots, the shadowing software automatically performs a merge operation on the shadow set.

Example 6-4 Merge Operation: Rebuilding a Shadow Set

$ SHOW DEVICES DSA5: Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA5: Mounted 0 GHOST 565997 1 1 $11$DUA21: (00NODE) ShadowMergeMbr 0 (merging DSA5: 0% merged) $11$DUA31: (YRNODE) ShadowMergeMbr 0 (merging DSA5: 0% merged)

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.

7.1 Upgrading the OpenVMS 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 7.3.2.
   • 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 7.3.4 for an example.
3. Enter the MOUNT/OVERRIDE=SHADOW_MEMBERSHIP command on the upgrade disk to erase the shadowing 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.

   Note 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> SET ENVIRONMENT/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.

   Note 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 before performing the upgrade. This requires changing SYSGEN parameter values interactively using the SYSGEN utility.

   
   Invoke SYSGEN by entering the following command:

   $ RUN SYS$SYSTEM:SYSGEN

   
   On OpenVMS Alpha systems, enter the following:

   SYSGEN> USE upgrade-disk:[SYSn.SYSEXE]ALPHAVMSSYS.PAR SYSGEN>

   
   On OpenVMS VAX systems, enter the following:

   SYSGEN> USE upgrade-disk:[SYSn.SYSEXE]VAXVMSSYS.PAR SYSGEN>

   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 volume shadowing on the system disk by setting the SYSGEN parameters SHADOWING and SHADOW_SYS_DISK to 0, as follows:

   SYSGEN> SET SHADOWING 0 SYSGEN> SET SHADOW_SYS_DISK 0

   
   On OpenVMS Alpha systems, enter:

   SYSGEN> WRITE upgrade-disk:[SYSn.SYSEXE]ALPHAVMSSYS.PAR

   
   On OpenVMS VAX systems, enter:

   SYSGEN> WRITE upgrade-disk:[SYSn.SYSEXE]VAXVMSSYS.PAR

   
   Type EXIT or press Ctrl/Z to exit from 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:

   $ RUN SYS$SYSTEM:SYSGEN SYSGEN> USE CURRENT SYSGEN>

   
   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):

   SYSGEN> SET SHADOW_SYS_DISK 1 SYSGEN> SET SHADOW_SYS_UNIT 54 SYSGEN> WRITE CURRENT

   
   Type EXIT or press Ctrl/Z to exit from 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 upgrade disk.
   3. Make sure the system parameters in the node-specific SYS$SYSTEM:MODPARAMS.DAT files are correct (as described in Section 3.2.1). 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 either 2 or 3, SHADOW_SYS_DISK to 1, and SHADOW_SYS_UNIT to the unit number of the system disk virtual unit. 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.
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 7.3. If you usually use standalone BACKUP at this point, refer to Section 7.3.1.

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