If a dynamic disk shows as "Foreign" in Volume Manager, it means that the disk has been moved from another installation of Volume Manager and its dynamic disk group does not match the one that already existed. To allow the disk to be recognized and made usable by the current installation of Volume Manager, right-click on the disk and select Merge Foreign Disk (Figure 1).

Figure 1 - Merge Foreign Disk
 

Because a volume can span more than one disk (e.g., a mirrored volume), it is important to first verify the disk configuration and move all the disks on which the volume resides.  If only part of the disk set is moved, the volumes will have a status of either "Failed Redundancy" or "Failed".