Back up the current boot volume

to the other disk

 You can utilize built-in Windows Server Backup feature to make a backup of the Disk4 which contains the operation system and then restore server operating system to the new disk by performing system recovery in the Windows PE environment. This is known as bare metal restore.

 Steps to perform a manual full backup of the server:

 1. Click Start, click Administrative Tools, and then click Windows Server Backup.

 2. From the Actions pane of the snap-in default page, under Windows Server Backup, click Backup Once. This opens the Backup Once Wizard.

 3. On the Backup options page, do one of the following, and then click Next:

 Click Different options.

 4. On the Select backup configuration page, Click Custom to back up just certain volumes, and then click Next. Then, on the Select backup items page, select the check boxes for the volumes that contain the operating system. And select Enable system recovery.

 Please Note

 Volumes that contain operating system components or applications are included in the backup by default to enable operating system recovery and system state recovery options.

 5. On the Specify destination type page, click Local drives, and then click Next.

 6. On the Select backup destination page, select the destination that you want to use to store the backup from the drop-down list. If you choose a hard disk, confirm that there is enough free space on the disk. If you choose a DVD drive or other optical media, indicate whether you want the contents to be verified after they are written to.

 7. On the Specify advanced options page, indicate whether you want to create a copy or full Volume Shadow Copy Service (VSS) backup. You should click VSS full backup if you are sure you are not using another product to create backups. Otherwise, you should click VSS copy backup. Click Next.

 8. On the Confirmation page, review the details, and then click Backup. The wizard prepares the backup set, formats the optical or removable media (if that is what you are using), and then creates the backup.

 9. On the Backup progress page, you can view the status of the backup. If you are backing up to a DVD, when the backup starts, you will receive a message to insert the first DVD in the drive and then, if the backup is too large for a single DVD, you will be prompted for subsequent DVDs as the backup continues. During this process, you should physically write the information next to Disk label in the message on the DVD that you insert. You will need this information later to perform a recovery.

 Steps to restore a server operation system:

 To recover your operating system or full server using a Windows Setup disc

 1. Insert the Windows Setup disc into the CD or DVD drive and turn on the computer. If needed, press the required key to boot from the disc. The Install Windows Wizard should appear.

 2. Specify language settings, and then click Next.

 3. Click Repair your computer.

 4. Setup searches the hard disk drives for an existing Windows installation and then displays the results in System Recovery Options. If you are recovering the operating system onto separate hardware, the list should be empty (there should be no operating system on the computer). Click Next.

 5. On the System Recovery Options page, click Windows Complete PC Restore. This opens the Windows Complete PC Restore Wizard.

 6. Do one of the following:

 a. Click Use the latest available backup (recommended) and then click Next.

 b. Click Restore a different backup and then click Next.

 7. If you chose to restore a different backup, on the Select the location of the backup page, do one of the following:

 a. Click the computer that contains the backup that you want to use, and then click Next.

 Please note:

 If the storage location contains backups of multiple computers, make sure that you click the row for the backups for the computer that you want to use. Then, on the Select the backup to restore page, click the backup that you want to use, and then click Next.

 b. Click Advanced to browse for a backup on the network, and then click Next.

 8. On the Choose how to restore the backup page, do the following optional tasks, and then click Next:

 a. Select the Format and repartition disks check box to delete existing partitions and reformat the destination disks to be the same as the backup. This enables the Exclude disks button. Click this button and then select the check boxes associated with any disks that you want to exclude from being formatted and partitioned. The disk that contains the backup that you are using is automatically excluded.

 Please Note:

 Unless a disk is excluded, data on it can be lost—regardless of whether it was part of the backup or whether it has volumes that are being restored.

 In Exclude disks, if you do not see all the disks that are attached to the computer, you might need to install the associated drivers for the storage device.

 b. Select the Only restore system disks check box to perform an operating system–only recovery.

 c. Click Install drivers to install device drivers for the hardware that you are recovering to.

 d. Click Advanced to specify whether the computer is restarted and the disks are checked for errors immediate after the recovery.

 9. Confirm the details for the restoration, and then click Finish.

If possible, please only make the Backup Disk and the new add disk online, make all the Disk arrays which contain data offline, and then reboot into Windows PE to perform the restore process.

During the bare metal restore process, please do not Select the Format and repartition disks check box. You may click Next and Select the Only restore system disks check box to perform an operating system–only recovery.

David Shen - MSFT
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After a couple hours of trying various configurations, I finally gave up on using the windows PC repair option. I made backups to a network drive, a local drive, and a DVD with the Windows server backup tool.  I tried taking all the disks out of the equation except the one to which I wanted to restore. Nothing helped, every time I'd get either data invalid or an element error.
So finally I popped in an old Ghost 11 CD, and I had no problem imaging one disk to the other directly. I then low-level formatted the suspected bad drive, and rebooted. The two disks appear to be mirroring up fine now. screenshot:
http://cid-6ca74493879dc944.skydrive.live.com/self.aspx/.Public/disks%7C_mirroring.PNG
One thing to note, the boot volume was no longer dynamic after I imaged it. Somehow Ghost had converted it back to basic. Of course adding the mirror forced a conversion back to dynamic. 
So I don't think I can actually mark any of these posts as an answer, since I could never get the backup tool to work as expected