For a host or host cluster to send I/O to a volume, you must assign the volume to the host or host cluster.
You can select a host or host cluster when you create a volume or you can assign a volume to a host or host cluster later. A host cluster is a group of hosts. You create a host cluster to make it easy to assign the same volumes to multiple hosts.
Assigning volumes to hosts is flexible, allowing you to meet your particular storage needs.
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Stand-alone host, not part of a host cluster — You can assign a volume to an individual host. The volume can be accessed only by the one host.
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Host cluster — You can assign a volume to a host cluster. The volume can be accessed by all the hosts in the host cluster.
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Host within a host cluster — You can assign a volume to an individual host that is part of a host cluster. Even though the host is part of a host cluster, the volume can be accessed only by the individual host and not by any other hosts in the host cluster.
When volumes are created, logical unit numbers (LUNs) are assigned automatically. The LUN serves as the "address" between the host and the controller during I/O operations. You can change LUNs after the volume is created.