Instructions at the two links below describe how to mirror an existing boot disk for Win2003 and Win2008 respectively:

https://technet.microsoft.com/en-us/library/cc783353%28v=ws.10%29.aspx

http://www.techotopia.com/index.php/Mirroring_Windows_Server_2008_R2_GBT_and_MBR_Boot_and_System_Disks

Both sets of instructions are substantially the same and both involve an xcopy step copy create a copy of the EFI files. However, numerous people (and now me) have reported that Windows reports a sharing violation when attempting to do this, on the EFI\Microsoft\Boot\BCD file. The entire operation is invalidated because of this sharing violation.

How to overcome it please?

Hi,

I assume you also found this article:

How to mirror the system and boot partition (RAID1) in Windows Server 2003

http://support.microsoft.com/kb/323432

I tried to build a dual boot system for test. The steps provided in above article are the same in Windows 2008 R2 or Windows 8. However as the way Windows boots up is changed in later versions, you will need to manually create the boot volume (system reserved volume) on second disk before creating the system mirror. 

Also you can create bootup entries with using BCDEdit instead of copy EFI files. Detailed steps could be found in this article:

Configuring Disk Mirroring for Windows Server 2008 R2

http://www.microsoft.com/en-us/download/details.aspx?id=23476

Thanks very much. The first article you cite was helpful. I couldn't use it directly because it doesn't seem to cover GPT disks, but the main clue is to skip some files, therefore I used the following robocopy syntax in place of the xcopy syntax mentioned above:

robocopy.exe s:\ t:\ * /e /copyall /dcopy:t /xf BCD.* /xd "System Volume Information"

By bypassing the BCD files as it does, the sharing violation is avoided. Presumably the omitted files are not needed - we'll see.

• Marked as answer by Danforth 8 hours 6 minutes ago