Figure 6-13 illustrates the concept of layers. Generally, changing the layer is only performed at initial setup time or as part of a major  reconfiguration. To change the layer of a FS9100 system, the system must meet the following  pre-conditions: Changing an FS9100 system from Storage layer to Replication layer can only be performed  by using the CLI. After you are certain that all of the pre-conditions have been met, issue the  following command: chsystem -layer replication Each system can be connected to a maximum of three other systems for the purposes of  Metro or Global Mirror. Partnership topologies GLYPH<SM590000> The FS9100 system must not have any system partnerships defined. If it is already using  Metro Mirror or Global Mirror, the existing partnerships and relationships must be removed  first. GLYPH<SM590000> The FS9100 system must not be visible to any other IBM Spectrum Virtualize, Storwize or  FS9100 system in the SAN fabric, which might require SAN zoning changes.  GLYPH<SM590000> The FS9100 system must not have any IBM Spectrum Virtualize, Storwize or FS9100 host  objects defined, and must not be virtualizing any other FS9100/Storwize controllers. Figure 6-13 Conceptualization of layers Chapter 6. Copy services  171