HP StorageWorks Clustered File System 3.2.1 Windows Storage Server Edition Administration Guide (February 2006)

Chapter 2: Introduction 10
A virtual host is a hostname/IP address configured on one or more servers.
The network interfaces selected on those servers to participate in the
virtual host must be on the same subnet. One server is selected as the
primary server for the virtual host. The remaining servers are backups.
The primary and backup servers do not need to be dedicated to these
activities; all servers can support other independent functions.
To ensure the availability of a virtual host, HP Clustered File System
monitors the health of all network interfaces and the health of the
underlying server. If you have created service or device monitors, those
monitors periodically check the health of the specified services or devices.
If any of these health checks fail, HP Clustered File System can transfer
the virtual host to a backup server and the network traffic will continue.
After creating virtual hosts, you will need to configure your network
applications to recognize them. When clients want to access a network
application, they use the virtual host address instead of the address of the
server where the application is running.
Service and Device Monitors
A service is a network service such as HTTP or FTP that is installed and
configured on the servers in the cluster. HP Clustered File System can be
configured to watch specific services with service monitors.
A service monitor is created on a virtual host. The service being
monitored should be installed on all servers associated with that virtual
host. When a service monitor determines that a service has failed, HP
Clustered File System transfers the virtual host for that service to a
backup server. For example, if the HTTP service fails, HP Clustered File
System will transfer the HTTP traffic to a backup server that provides
HTTP.
HP Clustered File System includes several built-in service monitors for
monitoring well-known network services. You can also configure custom
monitors for other services.
A device monitor is similar to a service monitor; however, it is assigned to
one or more servers. HP Clustered File System provides several built-in
device monitors.