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AdministeringIn addition to administering the database server, you can tune performance, replicate data, and archive data.
System administrationThese topics contain concepts, procedures, and reference information for database and database server administrators to use for managing and tuning HCL OneDB™ database servers.
Administrator's GuideThe HCL OneDB™ Administrator's Guide provides the information required to administer HCL OneDB™.
High availability and scalabilityA successful production environment requires database systems that are always available, with minimal if any planned outages, and that can be scaled quickly and easily as business requirements change.
Cluster failover, redirection, and restorationTo maintain availability, you must plan for the failover of primary servers, redirecting client connections from unavailable servers, and restoring the cluster to its original configuration after a failure.
Failover configuration for high-availability clustersA failure in a high-availability cluster means that one of the servers is no longer available. If a primary server fails, you must promote a secondary server to the role of primary server. Connection Managers can be configured to perform automatic failover.
Cluster failuresA high-availability cluster failure is a loss of connection between the database servers in a cluster that can be caused by several different situations.
Connecting offline servers to the new primary serverAfter failover, you must reconnect any offline secondary servers to the new primary server.

Connecting offline servers to the new primary server

After failover, you must reconnect any offline secondary servers to the new primary server.

If the primary server in a high-availability cluster fails, all online secondary servers are notified of the failure. The secondary servers connect to the new primary server and continue to operate. However, RS secondary servers and HDR secondary servers that are not online at the time of the failover do not receive the failover notification, and attempts to connect to the original (failed) primary server when the servers are back online. In this case, the primary server must be manually reset on those secondary servers.

Run the following commands on secondary servers that were offline when the failover occurred.

For HDR secondary servers:
```
oninit -PHY
onmode -d secondary new_primary
```
new_primary indicates the name of the current primary server.
For RS secondary servers:
```
oninit -PHY
onmode -d RSS new_primary
```
new_primary indicates the name of the current primary server.

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