Installation guide

Section 1.2:Cluster Features 9
1.2 Cluster Features
A cluster includes the following features:
• No-single-point-of-failure hardware configuration
Clusters can include a dual-controller RAID array, multiple network and serial communication
channels, and redundant uninterruptible power supply (UPS) systems to ensure that no single fail-
ure results in application down time or loss of data.
Alternately, a low-cost cluster can be set up to provide less availability than a no-single-point-of-
failure cluster. For example, an administrator can set up a cluster with a single-controller RAID
array and only a single heartbeat channel.
Note
Certain low-cost alternatives, such as software RAID and multi-initiator
parallel SCSI, are not compatible or appropriate for use on the shared
cluster storage. Refer to Section 2.1, Choosing a Hardware Configura-
tion, for more information.
• Service configuration framework
Clusters enable an administrator to easily configure individual services to make data and appli-
cations highly available. To create a service, an administrator specifies the resources used in the
service and properties for the service, including the service name, application start and stop script,
disk partitions, mount points, and the cluster system on which an administrator prefers to run the
service. After the administrator adds a service, the cluster enters the information into the cluster
database on shared storage, where it can be accessed by both cluster systems.
The cluster provides an easy-to-use framework for database applications. For example, a database
service serves highly-available data to a database application. The application running on a cluster
system provides network access to database client systems, such as Web servers. If the service
fails over to another cluster system, the application can still access the shared database data. A
network-accessible database service is usually assigned an IP address, which is failed over along
with the service to maintain transparent access for clients.
The cluster service framework can be easily extended to other applications, as well.
• Data integrity assurance
To ensure data integrity, only one cluster system can run a service and access service data at one
time. Using power switches in the cluster configuration enable each cluster system to power-cycle
the other cluster system before restarting its services during the failover process. This prevents