High-availability Cluster - Node Reliability

Node Reliability

HA clusters usually utilize all available techniques to make the individual systems and shared infrastructure as reliable as possible. These include:

• Disk mirroring so that failure of internal disks does not result in system crashes.
• Redundant network connections so that single cable, switch, or network interface failures do not result in network outages.
• Redundant storage area network or SAN data connections so that single cable, switch, or interface failures do not lead to loss of connectivity to the storage (this would violate the share-nothing architecture).
• Redundant electrical power inputs on different circuits, usually both or all protected by uninterruptible power supply units, and redundant power supply units, so that single power feed, cable, UPS, or power supply failures do not lead to loss of power to the system.

These features help minimize the chances that the clustering failover between systems will be required. In such a failover, the service provided is unavailable for at least a little while, so measures to avoid failover are preferred.