If you configure N+1 data protection on a cluster, and one node fails, all of the data is still accessible from every other node in the cluster. If the node comes back online, the node rejoins the cluster automatically without requiring a full rebuild.
To ensure that data remains protected, if you physically remove a node from the cluster, you must also logically remove the node from the cluster. After you logically remove a node, the node automatically reformats its own drives, and resets itself to the factory default settings. The reset occurs only after OneFS has confirmed that all data has been reprotected. You can logically remove a node using the smartfail process. It is important that you smartfail nodes only when you want to permanently remove a node from the cluster.
If you remove a failed node before adding a new node, data stored on the failed node must be rebuilt in the free space in the cluster. After the new node is added, OneFS distributes the data to the new node. It is more efficient to add a replacement node to the cluster before failing the old node because OneFS can immediately use the replacement node to rebuild the data stored on the failed node.