These terms are used in this chapter:
Cluster – multiple systems, or nodes, that work together as a single entity to provide applications, system resources, and data to users.
Cluster node – a physical machine that is part of a Sun Cluster. Also called a physical host.
Data service – an application that provides client service on a network and implements read and write access to disk-based data. Replication Server and Adaptive Server Enterprise are examples of data services.
Disk group – a well-defined group of multihost disks that move as a unit between two servers in an HA configuration.
Fault monitor – a daemon that probes data services.
High availability (HA) – very low downtime. Computer systems that provide HA usually provide 99.999% availability, or roughly five minutes unscheduled downtime per year.
Logical host – a group of resources including a disk group, logical host name, and logical IP address. A logical host resides on (or is mastered by) a physical host (or node) in a cluster machine. It can move as a unit between physical hosts on a cluster.
Master – the node with exclusive read and write access to the disk group that has the logical address mapped to its Ethernet address. The current master of the logical host runs the logical host’s data services.
Multihost disk – a disk configured for potential accessibility from multiple nodes.
Failover – the event triggered by a node or a data service failure, in which logical hosts and the data services on the logical hosts move to another node.
Failback – a planned event, where a logical host and its data services are moved back to the original hosts.
