Creating or removing change volumes

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Remote-copy change volumes create periodic point-in-time copies of either the primary volumes or the secondary volumes. You can use the command-line interface to create, change, or remove change volumes.

Change volumes can be used in a number of cases with relationships:
  • HyperSwap relationships and relationships with cycling modes set to Multiple must always be configured with change volumes.
  • Metro Mirror and Global Mirror with cycling mode set to None can optionally be configured with change volumes, which can be used to maintain a consistent secondary image when a relationship is resynchronized following an interruption to the replication.
For Global Mirror relationships with multiple cycling modes, changes are tracked and copied to intermediate change volumes at the primary site. The changes are transmitted to the secondary site continually to lower the bandwidth requirements, requiring only the average throughput not the peak. If you are changing either a Metro Mirror or Global Mirror relationship or consistency group to a Global Mirror with change volumes (cycling mode set to Multiple), you must create change volumes on both the master and auxiliary volumes that are used in the relationship or consistency group.

Using the command-line interface

  1. If the master and auxiliary volumes do not exist, use the mkvdisk command to create the change volumes. Master change volumes must be created with the following restrictions:
    • Master change volumes must be in the same I/O group.
    • Master change volumes must be the same logical size as the master volume of the relationship.
    • Master change volumes must be in the same storage pool as the master volume.
    This process is the same for auxiliary change volumes. When you assign a change volume to a relationship, the system creates new FlashCopy mappings between the master or auxiliary volume and the associated change volume. Therefore, sufficient available FlashCopy memory is needed in the target I/O group or the command fails.
  2. To create the change volume relationship on the master and auxiliary volumes, use the chrcrelationship command: 
    chrcrelationship -masterchange master_change_vdisk_id | master_change_vdisk_name rc_relationship_id|rc_relationship_name

    chrcrelationship -auxchange aux_change_vdisk_id | aux_change_vdisk_name rc_relationship_id|rc_relationship_name
  3. To remove change volumes, also use the chrcrelationship command:
    chrcrelationship -nomasterchange rc_rel_id | rc_rel_name
    chrcrelationship -noauxchange rc_rel_id | rc_rel_name
    The -masterchange and -nomasterchange parameters can be specified only when you run the chrcrelationship command on the master system for the relationship. The -auxchange and -noauxchange parameters can be specified only when you run the chrcrelationship command on the auxiliary system for the relationship.