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:
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