Amazon Redshift Multi-AZ is generally available for RA3 clusters

Amazon Redshift is announcing the general availability of Multi-AZ deployments for RA3 clusters. Redshift Multi-AZ deployments support running your data warehouse in multiple AWS Availability Zones (AZ) simultaneously and continue operating in unforeseen failure scenarios. A Multi-AZ deployment raises the Redshift Service Level Agreement (SLA) to 99.99% and delivers a highly available data warehouse for the most demanding mission-critical workloads.

Source:: Amazon AWS