Answer
High availability handles shorter continuity interruptions by keeping a secondary path ready. Disaster recovery handles the broader site, process, and business-recovery problem when facilities, networks, access paths, or wider dependencies fail. Some environments can prioritize one first, but many critical IBM i workloads eventually need both because uptime and recoverability are not the same promise.
Buyers should decide which consequence hurts more right now ... short outage, extended site loss, or both. That answer determines whether HA, DR, or a combined roadmap should come first.