ExpressCluster X 3.1 for Linux Getting Started Guide - Nec

Chapter 2 Using ExpressClusterFailover mechanismWhen an error is detected, ExpressCluster determines whether an error detected before failing overis an error in a server or a network partition. Then a failover is performed by activating variousresources and starting up applications on a properly working server.The group of resources which fail over at the same time is called a “failover group.” From a user’spoint of view, a failover group appears as a virtual computer.Note:In a cluster system, a failover is performed by restarting the application from aproperly working node. Therefore, what is saved in an application memory cannot befailed over.From occurrence of error to completion of failover takes a few minutes. See the figure 2-3 below:Error occurredError detectedFailover startedFailover completedHeartbeat timeoutFile systemrecoveredActivating resources(Including disks and IP addresses)Recovering or restartingapplicationFigure 2-3 Failover time chartHeartbeat timeout The time for a standby server to detect an error after that error occurred on the active server.The setting values of the cluster properties should be adjusted depending on the applicationload. (The default value is 90 seconds.)Activating various resources The time to activate the resources necessary for operating an application.The resources can be activated in a few seconds in ordinary settings, but the required timechanges depending on the type and the number of resources registered to the failover group.For more information, refer to the Installation and Configuration Guide.Start script execution time The data recovery time for a roll-back or roll-forward of the database and the startup time ofthe application to be used in operation.The time for roll-back or roll-forward can be predicted by adjusting the check point interval.For more information, refer to the document that comes with each software product.36ExpressCluster X 3.1 for Linux Getting Started Guide