This post is because while patching a Solaris 10 server with patch level Generic_142900-02 to Generic_142900-13.. There’s a need maintenance error on one of the sub mirror:
When a slice in a mirror or RAID5 metadevice device experiences errors,
DiskSuite puts the slice in the “Maintenance” state. No further reads or
writes are performed to a slice in the “Maintenance” state. Subsequent
errors on other slices in the same metadevice are handled differently,
depending on the type of the metadevice.
A mirror may be able to tolerate many slices in the “Maintenance” state and still be read from and written to. A RAID5 metadevice, by definition, can only tolerate a single slice in the “Maintenance” state. When either a mirror or RAID5 metadevice has a slice in the “Last Erred” state, I/O is still attempted to the slice marked “Last Erred”. This is because a “Last Erred” slice contains the last good copy of data from DiskSuite’s point of view.