Understanding Hyper-V Generations (Gen 1 & Gen 2)

Categories: Hyper-V, UEFI, VHD, GPT, BIOS, MBR, Physical Systems, Q-Hybrid, Restore, Alike v3, Alike v4


Microsoft introduced a new type of VM called “generation 2” or “gen 2” for short in Hyper-V 2012R2. Gen2 VMs use a variety of new/different hardware which in most cases make a Gen2 VM preferable to older formats. A few of the more important changes in Gen2 VMs:

  • UEFI Firmware
  • New virtual hardware for network adapters
  • New virtual hardware for input devices (mouse, PS/2 & i8042 keyboards)
  • New virtual hardware for video adapter
  • IDE controller replaced by SCSI controller
  • PCI Bus has been removed
  • Floppy drive support has been removed
  • New support for booting from SCSI drive or Network Adapter
  • GPT disk partitions supported
  • RemoteFX is no longer supported

Of special importance relating to your Alike interaction with Gen2 VMs, is that the newly supported UEFI/GPT boot and disk partition schemes of Gen2 systems are not supported by prior Hyper-V versions or by Citrix XenServer. This makes replication, or restoration of Gen2 VMs to an older Hyper-V, or XenServer host impossible. See below for more information.

Alike Support of Gen 2 VMs

Alike fully supports backup, restore, and replication of Gen2 VMs. However, Gen2 VMs protected by Alike can only be restored (as a bootable VM) to a hypervisor that supports UEFI/GPT (e.g. Hyper-V 2012R2 and up). Similarly, if you back up a UEFI/GPT physical machine using an Alike Physical license, you will only be able to restore and boot it off a Hyper-V 2012R2 environment.

Alike can always restore your backed up disks to VHD or VHDX file format. Alike also has file-level restore (FLR) that is not dependent on your hypervisor or your VM boot technology.

What is UEFI/GPT?

UEFI and GPT are distinct technologies, but they are usually grouped together when looking at boot technology. UEFI (Unified Extensible Firmware Interface) is a firmware alternative to BIOS boot that is more robust, but also more complex. Special firmware is required to handle UEFI, so only hardware built with UEFI support can handle booting an operating system that uses UEFI boot.

GPT (GUID Partition Table) is an alternative to MBR and is a newer way to format hard disk partitions. GPT is notable for its ability to handle larger partitions than MBR’s limit of 2TB. GPT has many other features as well, such as use of GUIDs to identify partitions and partition types, as well as support for a large number of partitions on a single GPT disk.

Gen 2 and UEFI/GPT

When a VM is built, the hypervisor must assign it virtual hardware so it can operate. Since UEFI/GPT requires different hardware than MBR, Microsoft created the gen 2 category to allow you to build machines that can boot under this scheme. If you choose gen 2, you cannot install a BIOS/MBR OS.

Microsoft also elected to require the VHDX virtual disk format for all gen 2 machines. For more information about VHD/VHDX, click here.

Backing up and Restoring Generations

Hyper-V gen 1 VMs can be backed up and restored to any platform Alike supports, including Hyper-V 2008R2, Hyper-V 2012, Hyper-V 2012R2, and Citrix XenServer. You can also restore gen 1 disks to the filesystem in either VHD or VHDX format.

Gen 2 VMs can only be restored and booted on environments that support UEFI/GPT. This is currently limited to Hyper-V 2012R2. If you attempt to restore or replicate a VM to another environment you will receive an error from Alike and your restore will fail, since the result, while containing all your data exactly as backed up, would not be bootable. You can always restore gen 2 VMs to the filesystem in VHDX or VHD format

Alike’s File-Level Restore (FLR) supports both GPT and MBR partition formats, meaning that you can restore files from either gen 1 or gen 2 VMs.

Physical Machine

Alike Physical supports backing up physical hosts using Q-Hybrid technology. Q-Hybrid supports both BIOS/MBR and UEFI/GPT systems. If you back up a physical machine that is UEFI/GPT, you cannot restore it to XenServer, Hyper-V 2008R2, or Hyper-V 2012, since these hypervisors do not support UEFI/GPT boot. You can restore it to Hyper-V 2012R2, to VHD/VHDX file, or using file-level restore.

Final Notes

Additional Resources:

Generation 2 Virtual Machine Overview

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