Thecus N8900 series User Manual page 127

After the Secondary server has communicated with Primary Server
successfully, then the state will changed to:
Click "Yes" to reboot both Primary and Secondary server.
If the communication has failed then you will see an error message as below.
Conditions in which the secondary server will take over to play the role as
Active:
1. Primary server RAID is damaged
2. Loss of the primary server's data port connection
3. Primary server goes down for any other reason
When the primary server encounters the above-mentioned situations, the
secondary server (PMS) will immediately take over to play the role as active. The
secondary server's system log will show "HA changed to active, getting resources",
and "Healthy: The RAID [HA] on system [PMS] is healthy now."
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