IBM Midrange System DS4000 Series Hardware Manual page 235

Define Additional Mapping option
Suppose that a particular host (or a host group) is already a part of a certain storage partition.
This means the logical drives are already mapped to that host or group. If you need to map
additional logical drives to the same host or group, use the Define Additional Mapping option:
1. Right-click the host or group to which you want to map a new logical drive. Select
Define Additional Mapping, as shown in Figure 4-84.
Figure 4-84 Define Additional Mapping
217
Chapter 4. IBM System Storage DS planning and configuration