I use and recommend Clonezilla to clone hard drives, but if you want to use clone and the original disk at the same time; you might have to change the Signature ID in a windows command prompt.

Type DISKPART from a command prompt to get in to the tool.

Inside the tool “list disk” will list the disks.

To do anything with a disk you must type “select disk <number>” where <number> is ### field from the “list disk”.

After you selected a disk you can “uniqueid disk” to list the signature id; and “uniqueid disk ID=<signature id>” where <signature id> is different than the ones you are currently using.

To get back to the command prompt from the DISKPART tool just type “exit”.

I don’t believe this can be changed in the Disk Management control, which you can open from the command prompt by typing “diskmgmt.msc”, however this tool will show you if the clone is offline via signature conflict.  After changing the signature with steps above you can use this tool to right click on disk (above the work offline, not on the partitions.)