Software RAID-1 in Windows server has a pitfall worth remembering: redundancy is working only when Windows is booted and is up & running. When machine is booting, it loads the OS from whichever drive is selected as first in the boot order in BIOS. If failing drive happens to be the first - the one from which Windows Server boots up, then two things needs to be done:
- BIOS settings have to be changed so that healthy secondary drive is used for booting, and
- Secondary Plex has to be selected as a default boot drive in Windows Startup & Recovery configuration.
Having Hyper-V adds even one more step. Hyper-V does something as the boot time, and is apparently enabled only on the first drive in the boot sequence. After you have made healthy secondary drive the first in boot sequence, secondary drive's boot routine needs to be manually adjusted to include loading Hyper-V, or you will get the dreaded, useless "Virtual machine could not be started because the hypervisor is not running" error when starting a virtual machine. To update your newly-selected boot drive for loading Hyper-V, run a Command Prompt as Administrator and execute following command:
bcdedit /set hypervisorlaunchtype auto
Reboot the server again - this time your secondary drive is bootable as far as BIOS concerned, secondary plex is used to boot windows, and Hyper-V is made to be loaded from the secondary drive too.