A cluster system provides high-availability by operating two or more servers as one virtual server.
If a system is run with only one server machine, and the server machine or the server application fails, all operations would stop until it is rebooted.
In a cluster system where two or more server machines are linked together, if the primary server machine becomes unusable due to an error on the server machine or the application being run, the secondary server machine can restart the application that was running on the failed server machine to resume the operation, reducing the operation stop time. The switchover from a failed server to another server is called failover.
These two or more linked server machines are referred to as a cluster of server machines and clustering server machines are referred to as nodes in the cluster system.
Clusters of server machines are classified into one of the following types.
Standby class
This is a cluster of standby nodes that stand ready to take over from operating nodes. The mode can be one of the following four modes.
1:1 standby
A cluster system consist one operating node and one standby node. The operating node is operational and the standby node stands ready to take over if needed. This operation mode ensures the continuous availability of cluster applications even after failover.
n:1 standby
A cluster consists of n operating nodes and one standby node. The n operating nodes run different operations and the standby node stands ready to take over from all of the operating nodes. This operation mode ensures the availability of cluster applications even after failover. It is also cost-effective because only one node serves as the standby node for cluster applications.
Mutual standby
A cluster consists of two nodes with both operating and standby applications. The two nodes run different operations and stand ready to take over from each other. If one of these nodes fails, the other node runs both of the operations. In this operation mode, two or more cluster applications will be operating on the failover node in the event of a node failure.
Cascade
A cluster consist three or more nodes. One of the nodes is the operating node and the others are the standby nodes. If the operating node fails, cluster applications are switched to one of the standby nodes. Even if a failover fails, cluster applications are moved to another standby node. When one node is stopped in the event of node failure or scheduled downtime such as system maintenance or upgrading, the redundant configuration can be maintained. This operation mode ensures the continuous availability of cluster applications.
Scalable class
This is a cluster that allows multiple server machines to operate concurrently for performance improvement and degradation. The difference from the standby class is that this class does not divide the nodes into the operating type and the standby type. If one of the nodes in the cluster fails, the operation is degraded to the other servers.
See
For details, refer to the version of "PRIMECLUSTER Installation and Administration Guide" for the respective operating System.
