Compaq ProLiant Clusters HA/F100 Administrator's Manual page 41

Designing the Compaq ProLiant Clusters HA/F100 and HA/F200 2-7
If the node running the order entry database encounters a failure, the database
fails over to its secondary node. The order entry clients experience a slight
disruption of service while the database resources are failed over, the database
transaction log is rolled back, and the information in the database is validated.
When the database validation is complete, the order entry application is
brought online on the file and print server and the clients can reconnect to it.
While the database validation is occurring, file and print activities continue
without disruption.
If the file and print server encounters a failure, those services are not failed
over to the order entry server. File and print services are offline until the
problem is resolved and the node is brought back online.
Active/Standby Configuration
The primary difference between an active/active configuration and an
active/standby configuration is the number of servers actively processing data.
In active/standby, only one server is processing data (active) while the other
(the standby server) is in an idle state.
The standby server must be logged in to the Windows NT or Windows 2000
domain and the Microsoft clustering software must be up and running.
However, no applications are running. The standby server's only purpose is to
take over failed clustered applications from its partner. The standby server is
not a preferred node for any clustered applications and, therefore, does not fail
over any applications to its partner server.
Because the standby server does not process data until it accepts failed over
applications, the limited use of the server may not justify the cost of the server.
However, the cost of standby servers is justified when performance and
availability are paramount to a business' operations.
The standby server should be designed to run all of the clustered applications
with little or no performance degradation. Since the standby server is not
running any applications while the cluster is in a normal operating state, a
failed-over clustered application will likely execute with the same speed and
response time as if it were executing on the primary server.