Taking Over From an Original Primary

The takeover procedure involves transferring the Primary role from an original Primary to a Secondary. When the original Primary fails or is destroyed because of a disaster, the takeover procedure enables you to convert a consistent Secondary to a Primary. The takeover of a Primary role by a Secondary is useful when the Primary experiences unscheduled downtimes or is destroyed because of a disaster.

Use the takeover procedure to transfer the Primary role from an original Primary to a Secondary. The takeover task must be performed on the Secondary host. The takeover task fails when performed on a Primary host.

The takeover procedure performs the following functions on the RDS to which the original Primary belongs:

• Converts the Secondary RVG to a Primary RVG.
• Removes the original Primary from the RDS.
• Enables the fast-failback feature on the new Primary depending on the failback option that you selected from the Takeover wizard. Each data volume in the Secondary RVG must have an associated Data Change Map (DCM) to enable fast failback with or without the autofailback. For more information on failing back, see Failing Back to the Original Primary.

Failback Options

The Takeover dialog box provides the following options to fail back to the original Primary. Select the required option depending on the method you plan to use for failback.

• Fast failback ---This is the default. Use this option when you want to incrementally synchronize the new Primary with the original Primary. This option enables fast failback; however, the original Primary is not automatically converted to a Secondary after reboot. To synchronize the data volumes on the original Primary and convert the original Primary to a Secondary, use the Replay Failback Log task (Change Role > Replay Failback Log) on the new Primary.
• The Auto fast failback option enables you to automatically synchronize the original Primary when it becomes available. This option converts the original Primary to a Secondary when the original Primary becomes available after an unexpected failure and also automatically synchronizes the data volumes on the original Primary, which is now the new Secondary, using fast failback. Each Secondary data volume must have an associated DCM.
• If No fast failback is chosen, you must synchronize the original Primary after it becomes available either using difference-based synchronization or full synchronization. Use the Synchronize RVG task (Tools > Synchronize RVG) to synchronize the original Primary using difference-based synchronization or full synchronization.

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 Tip    We recommend that you use the fast failback synchronization method to synchronize the original Primary with the new Primary. For instructions, see Failing Back Using Fast-Failback Synchronization.

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  To take over from the original Primary to the Secondary

1. Make sure that the data volumes on the Secondary host have associated DCMs if you want to use the fast failback logging feature.
2. From the Secondary RVG view on the Secondary host, choose Change Role > Takeover. The Takeover dialog box enables you to convert the selected Secondary to be the new Primary.

   

   Click the thumbnail above to view full-sized image.

3. Complete the Takeover Options page as follows:

   Options: Fast failback Auto fast failback No fast failback

   By default, Fast failback is selected. If this option is not appropriate, select the required option. To enable fast failback logging only, select Fast failback. You can synchronize the data volumes on the original Primary and convert the original Primary to a Secondary using the Replay Failback Log wizard (Change Role > Replay Failback Log). To convert the original Primary to a Secondary after it becomes available, and also automatically use the DCM to synchronize the data volumes on the original Primary using fast failback, select Auto fast failback. To change the role from Secondary to Primary without enabling fast failback, select No fast failback. Select this option if you are sure that the original Primary will not recover or if most of the data on the new Primary is going to change while the original Primary is unavailable.

4. Click OK to proceed with the Takeover operation. A message displays to indicate whether the takeover succeeded or failed.
5. Click Close.
6. Verify whether fast-failback is enabled. If it is, the dcm_logging flag is displayed in the Flags column of the Primary RLINK in Primary RVG view.
7. If the takeover succeeds, start the application on the new Primary. Starting the applications on the new Primary after a takeover may require an application recovery to be run.