content_image/971674.jpg
Figure 6-13 illustrates the concept of layers. 

<img src='content_image/971674.jpg'>

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: 

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. 

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 system partnerships defined. If it is already using Metro Mirror or Global Mirror, the existing partnerships and relationships must be removed first. 

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 

## Partnership topologies 

Each system can be connected to a maximum of three other systems for the purposes of Metro or Global Mirror. 

