2.8. General Configuration Considerations

Clusters can include a dual-controller RAID array, multiple bonded network channels, multiple paths between cluster members and storage, and redundant un-interruptible power supply (UPS) systems to ensure that no single failure results in application down time or loss of data.

Alternatively, a low-cost cluster can be set up to provide less availability than a no-single-point-of-failure cluster. For example, you can set up a cluster with a single-controller RAID array and only a single Ethernet channel.

Certain low-cost alternatives, such as host RAID controllers, software RAID without cluster support, and multi-initiator parallel SCSI configurations are not compatible or appropriate for use as shared cluster storage.

To ensure data integrity, only one node can run a cluster service and access cluster-service data at a time. The use of power switches in the cluster hardware configuration enables a node to power-cycle another node before restarting that node's cluster services during a failover process. This prevents two nodes from simultaneously accessing the same data and corrupting it. It is strongly recommended that fence devices (hardware or software solutions that remotely power, shutdown, and reboot cluster nodes) are used to guarantee data integrity under all failure conditions. Watchdog timers provide an alternative way to to ensure correct operation of cluster service failover.

Cluster quorum and node health is determined by communication of messages among cluster nodes via Ethernet. In addition, cluster nodes use Ethernet for a variety of other critical cluster functions (for example, fencing). With Ethernet channel bonding, multiple Ethernet interfaces are configured to behave as one, reducing the risk of a single-point-of-failure in the typical switched Ethernet connection among cluster nodes and other cluster hardware.