A SPARC M7-16 server is divided into four configurable units called DCUs. These DCUs have four CMIOUs each. Two of the DCUs are in the top CMIOU chassis, and two are in the bottom CMIOU chassis. You can configure DCUs into one to four PDomains.
Each CMIOU chassis also has two service processor proxies. SPP2 and SPP3 are in the top chassis, and SPP0 and SPP1 are in the bottom chassis. These SPPs have two service processor modules each. To achieve redundancy, each SPM (SPM0 and SPM1) on an SPP is assigned to a different DCU. SPM0 on each SPP manages one DCU in the CMIOU chassis, while SPM1 on each SPP manages the other DCU in the chassis.
Oracle ILOM identifies one of these SPMs as a DCU SPM to manage DCU activity. The other SPM runs Oracle ILOM, but remains inactive unless the DCU SPM can no longer manage the hardware. In this case, the inactive SPM assumes the role of the DCU SPM.
You cannot specify which SPMs will serve as DCU SPMs or the PDomain SPM, but you can specify that Oracle ILOM should assign a new SPM to serve each role. You might do this when, for example, you are replacing an SPP.
The switch chassis in the SPARC M7-16 server contains six switch units that allow CMIOUs to communicate with each other. The switch chassis also has two SPs (SP0 and SP1) that manage system resources. Each SP in the switch chassis has a single SPM (SPM0 in each SP). The SPM that you identify as the Active SP manages system resources unless it can no longer do so, in which case the Standby SP assumes its role.