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Gen 1 Vs Gen 2, BIOS Vs UEFI... The VM Wont BOOT

Solvedbootvirtualizationvm7 replies · 77 views · started
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Accepted solution by Diego Iqbal — lol same thing happened to me firmware mismatch is the most common cause. A disk with an MBR partition table needs BIOS/legacy boot (Hyper…
  1. Lars Sorensen
    @kernel_wrangler

    ugh. I've been tasked with converting it from a physical machine for an old server, now running on Hyper-V. Everything looked fine until I powered it on:

    Reboot and Select proper Boot device

    Reboot and Select proper Boot device
or Insert Boot Media in selected Boot device and press a key

No bootable device -- insert boot disk and press any key

    the virtual disk is attahced and the right size. the original machine booted fine yesterday. where did my OS go?

    i can see the disk in the VM settings, so its definitely attached. The original server is still around, powered off, so i can check settings there if needed. What usually goes wrong when moving an OS like this?

    4
  2. Felix Mori
    @shader_tinker831

    hmmm whats first in the VMs boot order right now?

    1 3 helpful
  4. Felix Mori
    @shader_tinker831

    yeahhh controller changes matter. A Windows guest that booted from IDE wont have the SCSI or VirtIO storage driver loaded at boot, sooo switching the controller gives an INACCESSIBLE_BOOT_DEVICE or no boot at all. Switch back, insatll the driver inside teh guest, then switch.

    1 12 helpful
  5. Diego Iqbal
    @diqbal

    After a conversion to UEFI, Windows can convert a disk in place with mbr2gpt /convert /allowFullOS, but only after validating with /validate 🔥 Do this on a copy or after a backup. lmk how it goes

    thinking

    15 14 helpful
  6. Diego Iqbal
    @diqbal
    Accepted solution

    lol same thing happened to me firmware mismatch is the most common cause. A disk with an MBR partition table needs BIOS/legacy boot (Hyper-V Generation 1), while a GPT disk with an EFI partition needs UEFI (Generation 2), check teh guest disk with any partition tool, then match the VMs firmware type. note u cant change the generation of an existing Hyper-V VM, so create a new VM with the right generation and attach the existing disk to it.

    0 6 helpful
  7. Diego Iqbal
    @diqbal

    alternatively keep teh old physical machine around until teh VM has been stable for a week. then changing the disk controller isnt a one-way door. just my 2 cents

    6 0 helpful
  8. Lars Sorensen
    @kernel_wrangler
    in reply to @diqbal

    @diqbal Switched back to IDE, installed teh storage driver in teh guest, then moved to SCSI. Boots fine now. Thanks, all. cant believe it was that simple lol

    15 0 helpful

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