If the Windows Server 2019 machines are in domain, then it's possible to use only two Server 2019 and one NAS server to create failover cluster. If you don't have domain environment, it's recommended to set a DC server before creating the cluster. Or you may choose workgroup failover cluster.
Hyper V replication is different from failover cluster:
Hyper V replication can do between two standalone Hyper V hosts, don't need to create a cluster. VM can replicate from Hyper V server 1 to Hyper V 2 server, and we will have two VM files. When S1 has issues, we can start VM on S2.
While in the failover cluster, the VM files are stored on shared storage, when S1 has issues, the ownership of the VM will failover to S2, S2 will get data of the VM in shared storage.
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