Using $MOUNT to Create and Mount Shadow Sets

You can create and mount shadow sets using the $MOUNT system service in a user-written program. Program calls to $MOUNT that create, mount, or add devices to shadow sets use the same syntax. To direct the system to perform any mount operation, you construct a $MOUNT item list. The item list specifies the virtual unit that represents the shadow set and the members (physical devices) that the shadow set contains.

The call to the $MOUNT system service has the following format:

SYS$MOUNT itmlst

Example 5-1 illustrates MACRO-32 statements that produce a $MOUNT system service item list to create and mount a shadow set.

Example 5-1 Item List to Create and Mount a Shadow Set

DSA23:  .ASCID /DSA23:/
MEMBER001:   .ASCID /$4$DUA9:/
MEMBER002:   .ASCID /$4$DUA5:/

VOLUME_LABEL:  .ASCID /MYVOLUME/
VOLUME_LOGNM:  .ASCID /DISK$MYVOLUME/

        .MACRO   .ITEM, SIZE, CODE, BUFFER, RETURN=0
        .WORD    SIZE, CODE
        .ADDRESS BUFFER, RETURN
        .ENDM    .ITEM

ITMLST: .ITEM   6,  MNT$_SHANAM, DSA23 
        .ITEM   8,  MNT$_SHAMEM, MEMBER001 
        .ITEM   8,  MNT$_SHAMEM, MEMBER002

        .ITEM   8,  MNT$_VOLNAM, VOLUME_LABEL  
        .ITEM   13, MNT$_LOGNAM, VOLUME_LOGNM  
         .LONG   0

The following list describes the elements in Example 5-1:

Notice that the virtual unit item descriptor occurs first. This item descriptor specifies DSA23 as the name of the virtual unit. See “Creating a Shadow Set ” for the proper naming syntax for the virtual unit and shadow set members.
The virtual unit item descriptor is followed by two member-unit item descriptors. Because Volume Shadowing for OpenVMS automatically determines the type of operation (copy or merge) necessary before disks can join a shadow set, all of the devices are mounted with MNT$_SHAMEM item descriptors. These item descriptors specify that the physical devices, $4$DUA9 and $4$DUA5, are to join the shadow set represented by DSA23.
The member item descriptors are followed by an item descriptor that specifies MYVOLUME as the volume label for the shadow set.
The last item descriptor specifies DISK$MYVOLUME as the logical name for the shadow set.

Later, if you want to add another device to the shadow set, you make another call to $MOUNT that specifies an item list that contains the name of the virtual unit and the name of the device you want to add to the shadow set. Example 5-2 shows how to add the physical device $4$DUA10: to the shadow set created in Example 5-1.

Example 5-2 Item List to Add a Member to a Shadow Set

DSA23:  .ASCID /DSA23:/

MEMBER003:  .ASCID /$4$DUA10:/
VOLUME_LABEL:  .ASCID /MYVOLUME/
VOLUME_LOGNM:  .ASCID /DISK$MYVOLUME/

        .MACRO   .ITEM, SIZE, CODE, BUFFER, RETURN=0
        .WORD    SIZE, CODE
        .ADDRESS BUFFER, RETURN
        .ENDM    .ITEM

ITMLST: .ITEM   6,  MNT$_SHANAM, DSA23  

        .ITEM   9,  MNT$_SHAMEM, MEMBER003
        .ITEM   8,  MNT$_VOLNAM, VOLUME_LABEL 
        .ITEM   13, MNT$_LOGNAM, VOLUME_LOGNM 
        .LONG   0

“$MOUNT Shadow Set Item Codes” briefly describes the $MOUNT shadow set item codes and discusses how to construct a valid $MOUNT item list. For a complete description of the $MOUNT service and all its item codes, see the HP OpenVMS System Services Reference Manual.