External LUs can have one of the following modes: External MDisks are discovered by the system as unmanaged MDisks. An unmanaged  MDisk is not a member of any storage pool. It is not associated with any volumes, and has  no metadata stored on it. The system does not write to an MDisk that is in unmanaged  mode, except when it attempts to change the mode of the MDisk to one of the other  modes. When unmanaged MDisks are added to storage pools, they become managed. Managed  mode MDisks are always members of a storage pool, and their extents contribute to the  storage pool. This mode is the most common and normal mode for an MDisk. Image mode provides a direct block-for-block translation from the MDisk to a volume. This  mode is provided to satisfy the following major usage scenarios: External MDisks can be managed through the External Storage pane, which is accessed by  clicking  Pools External Storage  (see Figure 6-28). To list all MDisks visible by the system with the CLI, use the  lsmdisk command without any  parameters. If required, output can be filtered to include only external or only array type  MDisks.  Add  Unmanaged  MDisks to an existing pool or create a pool to include them. If the storage  pool does not exist, follow the procedure that is described in 6.1.1, “Creating storage pools”  on page 216.  Figure 6-29 on page 234 shows how to add selected MDisk to a storage pool. Click  Assign under the Actions menu or right-click the MDisk and select  Assign . Chapter 6. Storage pools  233 Assigning MDisks to pools Listing external MDisks GLYPH<SM590000> Unmanaged GLYPH<SM590000> Managed GLYPH<SM590000> Image – Virtualization of external LUs that contain data that was not written through the IBM  SAN Volume Controller. – Exporting MDisks from the IBM SAN Volume Controller after migration of volumes to  image mode MDisks. Figure 6-28 External storage view