If a changeover cannot be performed, you should check the synchronization status of the servers as a Standby server can only switch to Main if it is synchronized.
To check the synchronization status:
- Log on to the Main server.
- Display the Server Status Tool by right-clicking on the server icon and selecting the Status option.
- Display the Standby>Links status information.
- Examine the Sync entry for each of the Standby servers. If the servers have not synchronized successfully, the Sync status will be No. This means that the standby servers cannot be synchronized with the Main server and so cannot switch to Main if required.
- Examine the Errors entries for the Standby servers. As the synchronization process has failed, the Errors entries will provide information about the cause of the failure(s). Common causes of synchronization errors include:
- Network failures—Use network monitoring tools such as ICMP Monitor points to check the status of the network between the Main and Standby servers.
- Server failures—Investigate any problems relating to the server hardware and software.
- Write failures (insufficient disk space on the Standby servers)—Free up some disk space on the Standby server or add extra disk space.
For more information on the status displays, see Links (Standby) in the Geo SCADA Expert Guide to the Server Status Tool.