System and Service Level Failover
Failover is the process specifically associated to cluster
systems. Typically it means when the Primary station of a cluster
system dies, the Secondary station will be activated to take over
the active duty of the Primary station. This feature supports the
high availability of the cluster server.
XLink's ClusterReplica Standard edition binds two Windows systems together
as the cluster server, which is best applicable for web server and
file servers. It will monitor the systems in the cluster system and the
pre-defined services to determine if the cluster system is in the
condition that a failover should be activated.
Failover conditions
ClusterReplica makes decisions on activation of failover on three
types of conditions:
- System failover - This happens when the entire Primary system
is down
- Service level failover - When any one of the monitored
services is not functioning normally
Detailed explanations of these conditions are listed below.
- System Level Failover
The first picture (1) below shows a normal working situation
of the cluster server. When the Primary station fails, the
Secondary Station will become the Primary station and work in
STAND ALONE mode as seen in picture (2).
- Service Level Failover
Failover will take place when one of the services fails to
function normally. In this situation, both clustered systems
will be running. However, their roles of ACTIVE and STANDBY will
be switched automatically.
NOTE: when the ACTIVE station is changed to become
the STANDBY Station, you know there is a service or application on that system
failed to function normally. You should exam the Secondary station and fix the
problem without delay. Resetting the cluster system is also important.
Here are some pictures to provide a general description of Failover (1)(2) and Failback (3)(4).
 
 
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