Has anyone actually used server 2012 R2 software mirroring to mirror the boot/system drive.

If so could you confirm that in the event of drive failure it does keep running on the mirrored drive and allow the server to be rebooted to the mirrored drive.

I seem to be getting differing answers to this question elsewhere. Some say the ridiculously convoluted procedure messing with BCD is necessary to do this but others report that disk management simply does it. Getting difficult to establish why it seems to work for some but not for others.



just test it on a VM with 2 vhd(x) if You are not sure.

I have one very old server with windows 2003 and mirroring enabled on system drive from disk management. It works. We had incidents where the first hard drive died. When You boot the system there is an option: boot from secondary plex.

We have been able to boot and make it work (it was 350km from us) just by asking someone who is non IT to pull the first drive out of the server. All was on place.

I believe it should work in 2012 if it worked in 2003 however this is just an assumption because we don't deploy from many years OS on hardware but on hypervisors and we always use hardware raid.

ps. I've just been curious and tested it on VM and everything looks fine it is rebuilding. Both disk shows as "boot". Screenshot from 2012 enter image description here

  • Thanks for trying that Bartłomiej. However there still seems to be some questions from others about whether this actually works or not in 2012. Guess I will have to do a test install and try it out.
    – NickC
    Jan 10 '14 at 21:09
  • @NickC by "works" do You mean reboot and try to boot from one or the other disk ? removing one trying from the other ? Jan 11 '14 at 8:56
  • By works I mean two things: 1). If either of the disks is removed while running it just continues using the other disk. 2). Either disk can be removed and the machine can still be booted using the other disk
    – NickC
    Jan 11 '14 at 12:35

Just testing this out for myself.

When converting the current system drive to dynamic I get the warning:

After you convert these disks to dynamic, you will not be able to start installed operating systems from any volume on these disks (except the current boot volume). Choose to ignore this and convert anyway.

However the option to mirror this drive (disk 0) is disabled. It does reboot ok but still no option to mirror the whole of disk 0. I think the option may have been present before it was converted to a dynamic disk but now that has been done I cannot see how to revert to a Basic disk without a complete reinstall.

Although I can't mirror the whole drive it seems I can mirror the System Reserve and C: partitions separately to disk 1, that seems to work.

Here is the result of testing this:

  • Disk 0 pulled out hot and windows still running
  • Reboot failed without disk 0, changed BIOS to boot from disk 1, now gets to Windows boot menu
  • need to select boot from secondary plex option then boots ok
  • shutdown and reboot with only drive 0 in, select primary plex and boots fine
  • shutdown and reboot with only drive 1 in, select secondary plex and boots fine
  • Reinsert both disks (boot from either via BIOS) but cannot rebuild the mirror

    Error: The plex is missing

  • Only method is to remove the mirrors and recreate

  • Which is fine except that an extra boot option gets added every time the mirror is recreated

    Windows Server 2012 R2 - Secondary plex – secondary plex

A final edit now that I have finished testing this:

It seems that after one mirrored drive is temporarily removed and Windows is booted to the other drive then when both drives are back Windows will not recognise the temporarily removed one just lists it in disk management as 'missing'.

This leads to it being necessary to break the mirrors to the 'missing' drive and recreate them which is fine except for the extra boot option which gets created every time.

Windows Server 2012 R2 - Secondary plex – secondary plex – secondary plex

  • - If You can specyfity in BIOS a primary and secondary disk to boot from that may solve Your problem. Some BIOSes allow to specify more than one disk as boot device some do not. Thats right You dont mirror drives -> You mirror volumes. Btw when You remove the first driver the second drive becomes primary so there should be no need to select 'boot from secondary plex'. It will boot from secondary but because it is alone it should be considered primary. Jan 11 '14 at 21:42
  • Unfortunately the BIOS on this HP DL380 only seems to use the first disk in the BIOS boot order to attempt to boot from.
    – NickC
    Jan 12 '14 at 20:12

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