User’s Guide186What are Primary controller and Secondary controller?The Primary and Secondary controllers are used to serve the hostcomputer’s I/O requests. Take note that the configurations andsettings can only be done on the Primary controller. The Secondarycontroller then synchronizes the configuration information of thePrimary controller, making the configurations of the Primary andSecondary controllers exactly the same.The controllers continuously monitor each other. When a controllerdetected that the other controller is not responding, the workingcontroller will immediately take over and disable the failed controlleruntil it has been replaced and enabled by user command.When should I choose Primary, Secondary or Autocfg mode?Generally Autocfg is the simplest way to configure the controllers. Bysetting each controller to Autocfg mode, the controllers will decideamong themselves which will be the Primary or Secondary controller.If you need to specify a particular controller as Primary or Secondary,you must set this manually.Limitations• Both controllers must use the same firmware version.• The time of the takeover process is about 5 seconds. Someoperating systems will not retry accessing the HDDs.• The cache memory will switch to Write-Through mode.• In firmware versions earlier than 2.11, only the primary controllerserves the host’s I/O request while the secondary controller justmonitors the primary controller continuously. In firmware version2.11 or later, both controllers can serve the host’s I/O request.
