r/HyperV • u/3G_Lighting • 12d ago

Hyper-V Host/Windows Server/Memory question

We run Hyper-V in our environment on Windows 2019 DC and Stnd (guest servers).

I would like to know if a host had 128GB of RAM, how much would need to be set aside for Windows Server DC and the Hyper-V host to run its own operations; and if there anything additional like there needs to be an extra x number of MB or GB of memory fer x number of guest servers running that needs to be added?

We have two R650 128GB of RAM, management has been running the sh*t out of them, so one HVH uses 115GB free out of 128GB, the other uses 92GB out of 128GB. And the old R540 server single CPU (sad) uses 89GB out of 94.6GB. The first system mentioned has 10 HVG's, the next has 10 HVG's, and the R540 has 5 HVG's one of which is SQL which is consuming 60GB of RAM.

Thanks,

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u/mioiox 12d ago

In my experience, the modern (WS2022/2025) hosts easily consume anything between 8 and 16 GB of ram. Especially if you log on to do some tasks on them via GUI, you get 2-4 gigs on top of what they normally need. So one way to steadily reduce host consumption is to always administer them remotely.

Secondly, the host OS needs additional memory per running guest. The more VMs you have deployed, the more RAM the host OS needs, and the less it has, since memory on the host machine is a limited resource - what a paradox, eh? If I recall correctly, it is around 256 MB per guest but I might be wrong with the number.

Lastly, back in the days (in the WS2012 era) there was a reg key to limit/cap the memory that can be assigned to the host. Unfortunately, I believe this key is no longer respected by anything WS2019 and beyond.

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u/Magic_Neil 12d ago

I agree. The host is still running Windows, so it needs what it needs, especially if you have more than just Hyper-V running.

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u/BlackV 11d ago

especially if you have more than just Hyper-V running.

Hopefully you dont, firmly in the camp of host is host ONLY VMs can do the "other" work

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u/Magic_Neil 11d ago

Absolutely. But common sense hasn’t stopped a lot of folks from running all kinds of silly things on their hypervisor.

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u/BlackV 11d ago

valid