Having multiple VMs running crashes system

[bfenty]

I have an Intel 12700K, 32GB of RAM, and. 3060TI in my desktop. I’m sharing that with a windows 11 vm that has passthrough on a nvme drive and the video card. It’s super stable and works great. UNLESS I also spin up my Linux VM with a VNC desktop-then they both crash within about 2 minutes of Linux getting to desktop, even with both running at idle. 
 

I believe I have not over provisioned(not even sure if that’s an issue assuming low actual usage?). I have selected separate cores on the processor for each. The RAM amount is less than 32GB total. It doesn’t seem like anything a problem until the desktop starts stuttering and then black screens and crashes. Both VMs crash according to web UI.
 

I don’t think there’s a reason I can’t run multiple VMs…I’d really like to be able to use Linux for development work and as a secure environment. Any help is appreciated. 

[JonathanM]

6 hours ago, bfenty said:

not even sure if that’s an issue assuming low actual usage?

It is an issue, usage doesn't matter, any RAM allocated is denied to the host completely. Try setting the windows to 8GB and the linux to 4GB and see how they perform.

[bfenty]

On 4/6/2024 at 3:32 PM, JonathanM said:

It is an issue, usage doesn't matter, any RAM allocated is denied to the host completely. Try setting the windows to 8GB and the linux to 4GB and see how they perform.

Yup that seems to have been the issue. I must have over provisioned it. Good solution, thank you. 
 

I ordered 64GB more RAM on a good deal, so I should be able to run a couple VMs simultaneously in the future. 

Edited April 7 by bfenty

[JonathanM]

35 minutes ago, bfenty said:

Yup that seems to have been the issue. I must have over provisioned it. Good solution, thank you. 
 

I ordered 64GB more RAM on a good deal, so I should be able to run a couple VMs simultaneously in the future. 

For best performance start at the lowest amount of RAM that will allow the VM to boot successfully, and add RAM in small chunks until the performance doesn't increase any more, then back it down to the last amount before it topped out. The host needs the RAM to emulate all the I/O and motherboard functions, so the more you can give to the host without slowing down the guest will give the best overall performance.

 

RAM allocated to the guest is totally gone from the hosts viewpoint, so the more you can give to the host the faster virtual hardware you will be running on. You wouldn't intentionally cripple a bare metal PC by giving it the slowest motherboard you could find and maxing out the RAM to compensate.

[bfenty]

Thanks for explaining. Do you know how much RAM is optimal for the host? Or at least a guideline? After my upgrade I’d like 32gb for my windows vm. 

[JonathanM]

14 hours ago, bfenty said:

Do you know how much RAM is optimal for the host?

As much as you can give it. The host RAM is used to cache disk access, so the more RAM it has, the better it will perform.

https://www.linuxatemyram.com/

[bfenty]

8 hours ago, JonathanM said:

As much as you can give it. The host RAM is used to cache disk access, so the more RAM it has, the better it will perform.

https://www.linuxatemyram.com/

Cool, so my plan to triple it will pay dividends. Thanks for the help!

BTW, for anyone reading this, I've definitely seen a performance IMPROVEMENT in my VM with less RAM allocated to it. That's counter-intuitive, but true. To JonathanM's point, I'm sure the bottlenecks I was experiencing were on the UNRAID side and not the VM side.

Edited April 8 by bfenty