In my domain environment I have a guest machine that acts as a file sever. I've recently purchased a new server for the purpose of implementing high availability between the 2 servers/sites. How can I go about implementing a failover cluster with the existing file server which already hosts shared folders along with implementing the new server.
Failover cluster requires shared storage, which has active-active replication between sites. You need SDS solution like S2D - https://docs.microsoft.com/en-us/windows-server/storage/storage-spaces/storage-spaces-direct-overview or StarWind VSAN https://www.starwindsoftware.com/resource-library/starwind-virtual-san-for-hyper-v-2-node-hyperconverged-scenario-with-windows-server-2016/
Cluster between sites has demanding network requirements, doesn’t matter, what shared storage you’ll use. For S2D – at least 10GbE, for StarWind – at least 1GbE, the latency up to 5ms. Also you’ll need to deploy a witness in 3rd site or in cloud to orchestrate failover in case of failure of storage network.
If your network does not meet the requirements, look at asynchronous solutions, like DFS-R - https://docs.microsoft.com/en-us/windows-server/storage/dfs-replication/dfsr-overview . Such approach doesn’t give you 100% data availability, but has lower requirements.