Availability controls: hardware redundancy (RAID, dual PSU), clustering (HA pairs), load balancing, geographic redundancy (multi-region), backups (offline/offsite), UPS/generators, automatic failover.
RAID improves storage availability but is NOT a backup. 3-2-1 backup rule: 3 copies, 2 media types, 1 offsite. RTO/RPO drive availability investment decisions. Chaos engineering proactively tests resilience by intentionally causing failures.