Creating and joining cluster is such a simple task in Proxmox. Another kudos to Proxmox team! They really made things too easy and boring.
However, there's a little caveat: every storage setting in Proxmox cluster is
synced cluster-wide. This causes confusion for many newcomers, which can be
seen on Proxmox forum. If you want a unique storage for a specifc node, you
MUST configure nodes first on the dialog.