Example - Taking over from an original Primary in a setup with multiple Secondaries


Example - Taking over from an original Primary in a setup with multiple Secondaries
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We recommend that you create RLINKs between the hosts london and tokyo when setting up the RDS.

In this example the Primary host seattle has failed. The example explains how to take over from the original Primary host seattle to the Secondary host london. This example also explains how to start replication from the new Primary london to the additional Secondary tokyo.

To take over from the Primary seattle to Secondary RVG on host london

Make sure that the Secondary is consistent by using the following command to check that the consistent flag is set:
```
# vxprint -l rlink_name
```
Make sure that the data volumes on the Secondary have associated DCMs.
```
# vxprint -g hrdg -ht hr_rvg
```
Make the Secondary RVG hr_rvg the new Primary RVG by typing the following command on the Secondary london:
```
# vradmin -g hrdg takeover hr_rvg
```
The vradmin takeover command enables fast failback.
Verify whether fast failback is enabled by typing the following command on the Secondary london:
```
# vxprint -l rlink_name
```
If fast failback is enabled, the dcm_logging flag is set.
If you had created RLINKs between the Secondary london and the additional Secondary tokyo, host tokyo is automatically added to the new configuration.
Otherwise, you must manually add tokyo as a Secondary to the new Primary london. To do this, create RLINKs between london and tokyo and associate them to the respective RVGs using the following commands.

On host london:
```
# vxmake -g hrdg rlink rlk_tokyo_hr_rvg local_host=london \
  remote_host=tokyo remote_rlink=rlk_london_hr_rvg \
  remote_dg=hrdg
# vxrlink -g hrdg assoc hr_rvg rlk_tokyo_hr_rvg
```
On host tokyo:
```
# vxmake -g hrdg rlink rlk_london_hr_rvg local_host=tokyo \
  remote_host=london remote_rlink=rlk_tokyo_hr_rvg \
  remote_dg=hrdg
 # vxrlink -g hrdg assoc hr_rvg rlk_london_hr_rvg
```
By default, the vxmake rlink command creates the RLINK with the protocol set to TCP/IP. If necessary, change the protocol to UDP/IP.
See Setting the network transport protocol for a Secondary.
Even after takeover, the RLINK from tokyo to the original primary seattle still remains attached. Detach this RLINK using the following command on the new Primary london or on the Secondary tokyo:
```
# vradmin -g hrdg stoprep hr_rvg tokyo
```
On the new Primary london:
- Synchronize the data volumes in the Secondary RVG hr_rvg on tokyo with the data volumes in the original Primary RVG hr_rvg using the difference-based synchronization and Storage Checkpoint. To do this, use the following command on any host in the RDS:
```
# vradmin -g hrdg -c checkpt syncrvg hr_rvg tokyo
```
  The -c option when used with the vradmin syncrvg command automatically starts a Storage Checkpoint with the specified name, checkpt, in this example. After the data volumes are synchronized, the Storage Checkpoint is ended.
- Start replication to tokyo using the Storage Checkpoint created above:
```
# vradmin -g hrdg -c checkpt startrep hr_rvg tokyo
```
Start the application on the new Primary london. Starting the applications on the new Primary after a takeover may require an application recovery to be run.

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