Storage Replica is a feature of Windows Server 2016, designed for the disaster recovery purposes. The replication it provides is block-level and volume-based. Storage Replica is targeted at disaster avoidance since the replication of data is done to a remote location.
Before, Windows had replication only at other levels, like file-to-file replication, applications replication, and VM-level replication. There was also block-level replication in the storage market, but vendor lock-in made it too expensive.
Storage Replica provides new opportunities for disaster recovery and disaster preparedness in the industry. With it, the data is synchronously protected at two separated sites, either different buildings, cities, or countries.
Storage Replica provides synchronous and asynchronous replication. With synchronous replication, the data is written to two locations simultaneously before completion of the IO, which is a way to go for mission-critical data. Asynchronous replication provides faster response time to application, so it comes in handy when the sites are too wide apart.
Read the full article here: https://www.starwindsoftware.com/blog/microsoft-storage-replica-in-a-nutshell