A host group is collection of one or more data hosts. The hosts in a host group access a storage array volume when the host group and the specified volume are included in a storage domain, which is a logical entity used to partition storage.
When you create a host group, the management software automatically includes it in the default storage domain. The default storage domain contains all hosts and host groups without explicit mappings and enables them to share access to volumes assigned a default logical unit number (LUN) mapping during volume creation. When you explicitly map a host group to a specific volume and LUN, the host group and volume are removed from the default storage domain and create a separate storage domain, which enables only the hosts in the group to share access to the specified volume.
A host group can be mapped to up to 256 volumes or snapshots. However, even though a host is a member of a host group, the individual host can be mapped to a separate volume, thus enabling one host to access more than one volume.