HP OpenVMS Systems Documentation

Content starts here Adding Shadow Set Members
HP Volume Shadowing for OpenVMS: OpenVMS Version 8.4 > Chapter 4 Creating and Managing Shadow Sets Using DCL Commands

Adding Shadow Set Members

Once a shadow set is created, you can add and remove individual members by mounting or dismounting physical disk devices. The shadowing software allows you to add and remove shadow set members at any time, transparently to user processes or applications running on the system.

Adding a Disk to an Existing Shadow Set

The following command shows how to add the disk $4$DUA3 to the DSA23 shadow set:

$ MOUNT/CONFIRM/SYSTEM DSA23: /SHADOW=($4$DUA9,$4$DUA3)volume-label

The command specifies both the currently active shadow set member ($4$DUA9) and the new member ($4$DUA3). Although it is not necessary to include them when mounting additional physical devices, you can specify current shadow set members without affecting their membership state.

Note that when you add volumes to an existing shadow set mounted across an OpenVMS Cluster system, the shadowing software automatically adds the new members on each OpenVMS Cluster node.

Creating a Two-Member Shadow Set and Adding a Third Member

Example 4-4 shows how to create a two-member shadow set with the first command and how to add another member to the shadow set with the second command.

Example 4-4 Creating a Shadow Set and Adding Third Member

%MOUNT-I-SHDWMEMSUCC, _$3$DIA7: (DISK300) is now a valid member of
the shadow set
%MOUNT-I-SHDWMEMSUCC, _$3$DIA8: (DISK301) is now a valid member of
the shadow set

%MOUNT-I-SHDWMEMCOPY, _$3$DIA6: (DISK302) added to the shadow set
with a copy operation

In this example, the first command creates a shadow set whose virtual unit name is DSA4. The member disks are $3$DIA7 and $3$DIA8. The second command mounts the disk $3$DIA6 and adds it to shadow set DSA4. The shadow set now includes three members: $3$DIA6, $3$DIA7, and $3$DIA8. In this example, when you add $3$DIA6 after the shadow set already exists, the added volume becomes the target of a copy operation.

Checking Status of Potential Shadow Set Members With /CONFIRM

When you add a disk to an existing shadow set, a copy operation is necessary. Volume shadowing automatically performs the copy operation, unless you use the /CONFIRM qualifier or the /NOCOPY qualifier. When you specify the /CONFIRM qualifier, as shown in Example 4-5, the MOUNT command displays the targets of copy operations and prompts for permission before the operations are performed. This precaution can prevent the erasure of important data. For more information about copy operations, see Chapter 6.

Example 4-5 Using the /CONFIRM Qualifier

%MOUNT-F-SHDWCOPYREQ, shadow copy required
Virtual Unit - DSA23 Volume Label - SHADOWVOL
 Member                    Volume Label Owner UIC 
 $1$DUA6: (LOVE)           SCRATCH      [100,100]
Allow FULL shadow copy on the above member(s)? [N]:NO 

This command instructs MOUNT to build a shadow set with the specified devices and to prompt for permission to perform any copy operations.

Because a copy operation is necessary, the virtual unit name and the volume label are displayed.

The display also includes the physical device name, the volume label, and the volume owner of the potential shadow set member that requires the copy operation.

A response of No causes MOUNT to quit without mounting or copying.

Checking Status of Potential Shadow Set Members With /NOCOPY

When you specify more than one disk, the shadowing software automatically determines the correct copy operation to perform in order to make shadow set members consistent with each other (see “Copy Operations” for details). The Mount utility interprets information recorded on each member to determine whether a member requires a copy operation, a merge operation, or no copy operation. If you are not sure which disks might be targets of copy operations, you can specify the /CONFIRM qualifier or the /NOCOPY qualifier as a precaution against overwriting important data when you mount a disk. With the /NOCOPY qualifier, you disable the copy operation.

Example 4-6 shows how to use the /NOCOPY qualifier to check the status of potential shadow set members before any data is erased.

Example 4-6  Using the /NPCOPY Qualifier

$MOUNT/NOCOPY DSA2: /SHADOW=($1$DUA4:,$1$DUA6:,$1$DUA7:) -
%MOUNT-F-SHDWCOPYREQ, shadow copy required
%MOUNT-I-SHDWMEMFAIL, DUA7: failed as a member of the shadow set
%MOUNT-F-SHDWCOPYREQ, shadow copy required 
$ MOUNT/COPY DSA2: /SHADOW=($1$DUA4:,$1$DUA6:,$1$DUA7:) -
%MOUNT-I-SHDWMEMSUCC, _$1$DUA4: (VOLUME001) is now a valid member of
the shadow set
%MOUNT-I-SHDWMEMSUCC, _$1$DUA6: (VOLUME002) is now a valid member of
the shadow set
%MOUNT-I-SHDWMEMCOPY, _$1$DUA7: (VOLUME003) added to the shadow set
with a copy operation 

The first command in this example instructs MOUNT to build a shadow set, with the specified devices, but only if a copy or merge operation is not required.

In this example, MOUNT did not build the shadow set because the specified disk, loaded on device $1$DUA7, required a copy operation. At this point, you can verify that the volume in device $1$DUA7 does not contain any useful data.

If the device does not contain valuable data, you can reenter the MOUNT command, as shown in this example, and include the /COPY qualifier. This command instructs MOUNT to mount a shadow set and to proceed with the necessary copy or merge operation.

The resulting MOUNT status messages show that the shadow set is successfully mounted. The $1$DUA7 device is currently the target of a copy operation; it attains full shadow set membership when the copy operation completes.