A high-availability Synology NAS is a combination of two Synology servers in a single, highly available cluster. One server takes on the role of the active server, while the other acts as a passive standby server. The active server handles all requests and data services, with everything continually replicated on the passive server. If the active server is unavailable, the passive server automatically takes over to keep the applications' file services running within minutes. In this way, this infrastructure ensures perfect data redundancy in the event of unforeseen events.