4. If you prepared a SAS host (as described in 5.3, “Preparing the host operating system” on  page 219), the WWPNs that you recorded in this section appear. If they do not appear in  the list, verify that you completed all of the required steps and check your cabling. Then,  click  Rescan  in the configuration wizard. Ensure that the ends of the SAS cables are  aligned correctly. 5. Under the  Optional Fields  section, you can set host type, the I/O groups that your host  can access, and the host cluster the host belongs if it is defined.  6. Click  Add Host  and a task completion window opens. 7. Click  Close  to return to the host view, which now lists your newly created host object, as  shown in Figure 5-69. 8. Repeat these steps for all of your SAS hosts. Note:  You can enter WWPNs manually. However, if these WWPNs are not visible to the  IBM Storwize V5000, the host object appears as offline and it is unusable for I/O  operations until the ports are visible. Important:  Host objects must belong to the same I/O groups as the volumes that you  want to map. Otherwise, the volumes are not visible to the host.  The IBM Storwize V5000 supports a maximum of four nodes per system. These nodes  are arranged as two I/O groups per cluster. Because of the host object limit per I/O  group, for maximum host connectivity, it is best to create hosts that use single I/O  groups. You can choose the host type. If you use HP/UX, OpenVMS, or TPGS, you must configure  the host. Otherwise, the default option ( Generic ) is acceptable. After all of the host objects are created, see Chapter 6, “Volume configuration” on page 309 to  create volumes and map them to the hosts. IBM Spectrum Virtualize software supports host clusters starting with version 7.7.1. A  host  cluster  is a group of logical host objects that can be managed together. For example, you can  create a volume mapping that is shared by every host in the host cluster. The systems use  internal protocols to manage access to the volumes and ensure consistency of the data. Host  objects that represent hosts can be grouped in a host cluster and share access to volumes. Volume mappings can either be shared or private: GLYPH<SM590000> Shared mappings are volume mappings that are shared among all the hosts that are in a  host cluster. When a host cluster is created, any common volume mappings become  shared among all the hosts within the host cluster.  Figure 5-69 Hosts view lists the newly created host object 5.6 Host Clusters 280  Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.2.1