The ASM instance ensures that any disk in a newly created disk group is addressable and is not currently a member of another disk group. You must use FORCE only when adding a disk that was dropped FORCE. If a disk is dropped NOFORCE, then use can add it NOFORCE. For example, a disk might have failed and was dropped from its disk group. After the disk is repaired, it is no longer part of any disk group, but ASM still recognizes that the disk had been a member of a disk group. You must use the FORCE flag to include the disk in a new disk group. In addition, the disk must be addressable, and the original disk group must not be mounted. Otherwise, the operation fails.