When installed in the proper slots, CMIOUs are designed to provide redundant access to the SP. Always install two CMIOUs in the first two slots of a SPARC M8-8 and SPARC M7-8 PDomain or a SPARC M7-16 DCU. Always follow these CMIOU configuration guidelines:
For example, ensure that there are CMIOUs installed in slots CMIOU_0 and CMIOU_1 in a SPARC M8-8 server with one PDomain. In this example, if one of the CMIOUs has faulted, the PDomain will still be able to access the SP through the other CMIOU.
If there is only one CMIOU is installed a PDomain or DCU, the communication link between the SP and the PDomain will be lost if the CMIOU faults or is taken offline. For example, if a SPARC M8-8 server with one PDomain contains one CMIOU installed in CMIOU_0, and that CMIOU goes offline or faults, the communication link between the Active SP and the CMIOU also goes down. In this example, the FMA fault information will not be synchronized between the Active SP and the PDomain host, the prtdiag command will not display environmental information, and the Oracle VM Server for SPARC software cannot save or read saved configuration information saved on the SP. Additionally, if the boot pool devices are on the CMIOU, the PDomain host might not be able to boot the Oracle Solaris OS.