Cluster Terminology; Nodes; Cluster Service; Shared Disks - HP Rx2620-2 - Integrity - 0 MB RAM Installation And Configuration Manual

Figure 1-1 NLB Example

Cluster Terminology

A working knowledge of clustering begins with the definition of some common terms. The
following terms are used throughout this document.

Nodes

Individual servers or members of a cluster are referred to as nodes or systems (the terms are
used interchangeably). A node can be an active or inactive member of a cluster, depending on
whether or not it is currently online and in communication with the other cluster nodes. An
active node can act as host to one or more cluster groups.

Cluster Service

Cluster service refers to the collection of clustering software on each node that manages all
cluster-specific activity.

Shared Disks

Shared disks are devices (normally hard disk drives) that the cluster nodes are attached to by a
shared bus. Applications, file shares, and other resources to be managed by the cluster are stored
on the shared disks.

Resources

Resources are physical or logical entities (such as file shares) managed by the cluster software.
Resources can provide a service to clients or be an integral part of the cluster. Examples of
resources are physical hardware devices such as disk drives, or logical items such as IP addresses,
network names, applications, and services. Resources are the basic unit of management by the
cluster service. A resource can only run on a single node in a cluster at a time, and is online on
a node when it is providing its service on that node.
At any given time, a resource can exhibit only one of the following states:
• Offline
• Offline pending
• Online
• Online pending
• Failed
When a resource is offline, it is unavailable for use by a client or another resource. When a
resource is online, it is available for use. The initial state of any resource is offline. When a resource
is in one of the pending states, it is in the process of either being brought online or taken offline.
14 Introduction