Oracle Message ORA-15040 - diskgroup is incomplete

ERRORdiskgroup is incomplete
CAUSESome of the disks comprising a diskgroup were not present.
ACTIONCheck the hardware to ensure that all disks are functional. Also check that the setting of the ASM_DISKSTRING initialization parameter has not changed. Alternatively, for normal or high redundancy diskgroups, use MOUNT FORCE to offline missing disks as part of mounting the diskgroup.