What is the default cluster?
The default cluster is a system-defined entity that allows any unassociated host port identifier that has logged into the storage array to gain access to volumes assigned to the default cluster. An unassociated host port identifier is a host port that is not logically associated with a particular host, but is physically installed in a host and logged into the storage array.
If you want hosts to have specific access to certain volumes in the storage array, you must not use the default cluster. Instead, you must associate the host port identifiers with their corresponding hosts. This task can be done either manually during the Create Host operation or automatically using the host context agent (HCA) installed on each host. Then, you assign volumes either to an individual host or to a host cluster.
You should only use the default cluster in special situations where your external storage environment is conducive to allowing all the hosts and all the logged-in host port identifiers connected to the storage array have access to all of the volumes (all-access mode) without specifically making the hosts known to the storage array or the user interface.
Initially, you can assign volumes only to the default cluster through the command line interface (CLI). However, after you assign at least one volume to the default cluster, this entity (called Default Cluster) is displayed in the user interface where you can then manage this entity.