Now, we have some idea about how to measure the availability level for a server; increasing the availability is very important for us. Is it possible for Proxmox to deal with this task? Yes, of course, but it is only available in cluster mode. The basic difference between single instance versus clusters under Proxmox is as follows:

Unlike running with a single Proxmox instance, we need to provide shared storage for the cluster to keep the data of virtual machines. In our configuration, we would like to use a package called DRBD, which allows us to use local storage from both servers to form a shared RAID 1 storage. The data synchronization will automatically be managed by the DRBD package. So, we don't need to purchase additional network storage for our testing.