You manage the storage systems of the SE server in the tree structure: Hardware -> Storage.
The Storage menu provides an overview of the storage available, and enables access to the Storage Manager in order to manage the storage.
If the SE server has more than one MU or if more than one SE server form a Management Cluster, the Storage menu provides an overview of the storage available in the complete configuration.
If you have an SE server configuration with multiple MUs, a submenu is displayed in the tree structure below Storage, which has an entry Storage (<mu-name>) for each MU on which the StorMan add-on pack is installed.
These entries give you an MU specific overview over the available storage and the direct access to the Storage Manager on the respective MU.