Hyper-V: Gen1 or Gen2?

I am configuring a new Hyper-V host and 2 Hyper-V child machines. All are Windows 2022 Servers.
Should I choose Generation 1 or Generation 2 when creating the VMs?

configure them as Gen 2

Should I create a generation 1 or 2 virtual machine in Hyper-V? | Microsoft Docs

Thanks. I see that Gen2 installs less virtual devices and is potentially faster. Are there any other upsides? What are the downsides?

Also, should I setup the VHDX disk as Fixed or Dynamic?

Always use Gen2 unless there’s a very specific reason to use Gen1, they support UEFI and are much more modern in general. Some stuff will need a Gen1 VM but they’re few and far between now.

For VHDX, that’s your choice based on storage, and there’s pros and cons to each

Fixed will result in faster performance at the cost of ballooning the disk to the maximum size at creation. If you make a 240GB disk, it’ll consume 240GB on the host’s storage with a fixed disk. This will also take some additional time during VM creation and isn’t the default.

Dynamic will create the disk much smaller and then expand it as it is filled with a buffer. This will be slower on expansion because the disk has to be ballooned on the fly. The advantage here is it will only consume as much space as the VM has free plus a buffer. If your VM consumes 64GB the disk will consume nearly that on the host’s storage. The disk is much quicker to create during VM creation though and is the default.

Other hypervisors and storage tech calls this thin and thick provisioning, dynamic is thin and fixed is thick.

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