The wizard concatenates the target name to the end of the source VDisk name and then concatenates a sequence number at the end of that string to create the new VDisk names. The maximum supported length for VDisk names is 15 characters. The VDisk that you have selected is not eligible to be used as the source VDisk for this wizard because it is already at the maximum supported length, and the concatenation would result in a VDisk name length that exceeds the maximum supported length.
Select a VDisk with a name length that supports the concatenation of the target name and sequence number when you submit this task.