Using the full synchronization feature

This section explains how to use the Full Synchronization feature of VVR to synchronize the Secondary completely and start replication. Full synchronization compresses zeroes while processing the data and hence proves beneficial when a large part of the Primary data volumes contain zeroes. However, we recommend that you use Automatic Synchronization to synchronize the Secondary because its performance is better than Full Synchronization. Automatic Synchronization also handles network outages efficiently and continues even after the system reboots.

Full synchronization synchronizes the Secondary over the network when the Primary data volumes contain data and when the application is active or inactive. After the Primary and Secondary are synchronized, replication must be started.

By default, the vradmin syncrvg command synchronizes Secondary data volumes using difference-based synchronization. To perform a full synchronization, specify the -full option.

We recommend that you always use the -c option with the vradmin syncrvg command to synchronize the Secondary using full synchronization. The -c checkpoint option starts a Storage Checkpoint, synchronizes the data volumes, and ends the Storage Checkpoint after the synchronization completes. After the vradmin syncrvg command completes, use this Storage Checkpoint with the vradmin startrep command to start replication. To delete the Primary Storage Checkpoints, use the vxrvg checkdelete command.

The SRL must be large enough to hold the incoming updates to the Primary data volumes while the synchronization is in progress. The SRL might fill up and the Storage Checkpoint might overflow if the number of writes to the Primary data volumes is high when the Secondary is being synchronized.

A Storage Checkpoint that has overflowed becomes invalid and cannot be used to start replication. If the Storage Checkpoint overflows while synchronization is in progress, the vradmin syncrvg command must be issued again.

The vradmin syncrvg command can be used to synchronize multiple Secondaries at the same time. The vradmin syncrvg command displays the progress of the synchronization.

The vradmin syncrvg command synchronizes the volumes in an RVG. If a volume set is associated to an RVG, synchronizing the RVG only affects the component volumes of the volume set that are associated with the RVG. If the volume set includes component volumes that are not associated to the RVG, those volumes are not synchronized.

See About SmartMove for VVR.

To synchronize the Secondary RVG with the Primary RVG using full synchronization with Storage Checkpoint

  1. Verify that the RLINKs are detached to ensure that replication is stopped.
  2. To synchronize the Secondary RVG, issue the following command:
    # vradmin -g diskgroup -full -c checkpt_name syncrvg \  
        local_rvgname sec_hostname....

    Note that you can use the -c option with the vradmin syncrvg command when performing full synchronization, to automatically start a Storage Checkpoint with the specified name. After the data volumes are synchronized, the Storage Checkpoint is ended. This Storage Checkpoint can then be used to start replication using the vradmin startrep command.

    The argument local_rvgname is the name of the RVG on the local host and represents its RDS.

    The argument sec_hostname... is a space-separated list of the names of the Secondary hosts as displayed in the output of the vradmin printrvg command.

    The argument checkpt_name specifies the name of the Primary Storage Checkpoint of your choice.

  3. After the synchronization completes, start replication to the Secondary with the Storage Checkpoint:
    # vradmin -g diskgroup -c checkpt_name startrep \
     local_rvgname sec_hostname
    

    After the RLINKs are attached, the Secondary remains inconsistent until it has received all of the accumulated updates up to the checkend. While the Secondary is inconsistent, the inconsistent flag is set on the Secondary RLINK. After all updates up to the checkend have been received and applied at the Secondary, the inconsistent flag is cleared.

    Use vxrlink status to view the status of synchronization.

    See Displaying the status of a Secondary.