Glossary
HA
High Availability, keeping a second system continuously synchronized so it can take over production workload within seconds to minutes of a failure.
HA is distinct from backup: a backup restores data after a loss, often over hours; HA keeps a live, synchronized second system ready to fail over to almost immediately. That readiness is what HA software licensing (PowerHA, Maxava, Rocket iCluster) is priced for.