When you replace the SPM in your server, you must install a fallback miniroot image that corresponds to the version of Oracle Solaris that are using. The miniroot image is not part of the OS or firmware image that you install. Also, you must update the miniroot image when you install a new version of Oracle Solaris on the server, so the fallback image matches that version and SRU of Oracle Solaris.
You must download the fallback miniroot image for your hardware and your Oracle Solaris version from My Oracle Support at https://support.oracle.com. Then follow the procedure "Uploading a New Solaris Miniroot Package From SP to Host" in the Oracle ILOM Administrator's Guide for Configuration and Maintenance.
You will see the defect.ilom.fs.miniroot-missing error if you fail to install a fallback miniroot image. For example:
-> show faulty
Target | Property |Value
-------------------------+--------------------------+---------------------------------------
/SP/faultmgmt/0 | fru | /SYS
/SP/faultmgmt/0/faults/0 | class | defect.ilom.fs.miniroot-missing