I had a 2 TB disk with a unique volume (on one single partition), containing data.

I did add a new 2 TB disk to be used as a mirror of the existing one. I went into the Disk Management tool to “add Mirror” but found that this option was not available. The menu was disabled:

First thing to check: the two disks to be used must be “Dynamic”. Right-click on “Disk x” to “Convert to Dynamic Disk …”.

Next, to be able to create a mirror, the system needs some free space to create its own reserved partition on the disk. So, right-click on the Volume of the disk with data to “Shrink Volume…” (Try first with 1 Mb). Once the disk has been shrunk, the menu “Add Mirror…” becomes accessible.

Et voilà.

NB.:

• It does not matter if the disks are MBR or GPT.
• Once the volume shrunk, you will possibly have to reboot.
• If you encounter an issue while adding a mirror, do a “Check Disk” (Properties > Tools > Check).
• If you can really not get rid of the error “DiskPart has referenced an object which is not up-to-date.” although rebooting, do an “Extend Volume” of 1 MB! (Sound silly, I know…) and then “Add Mirror”.
• In my case, while the disks were re-syncing, I did remove the mirror, did an “Extend Volume” to reuse the whole free space, and was still able to do an “Add Mirror”.
• MS Partition & Volume Info here.

Mirror using DiskPart

• Run DiskPart in a cmd prompt started as Administrator
• list disk
• select disk x [x=disk containing the volume to be mirrored]
• list volume
• select volume x [x=volume to be mirrored]
• add disk x [x=disk to be used for mirroring]