I'm going to build an Unraid system with a quad core i7. I'd like to give one VM 3 cores (plus the associated hyperthreaded cores), which only leaves one actual core for the second VM.

 

This is less than ideal, so what I have in mind is:

- VM1 gets cores 1-3 (plus hyperthreaded cores)

- VM2 gets cores 3-4 (plus hyperthreaded cores)

 

I wouldn't really have both computer doing a lot of work at the same time, but they would be running together most of the day.

 

Would this have any downsides? I assume it's not ideal for VM performance, but I've done similar things in VMWare before without really noticing it.

Would this have any downsides? I assume it's not ideal for VM performance, but I've done similar things in VMWare before without really noticing it.

 

If it worked on VMware it should work on KVM as well.

Would this have any downsides?

You didn't leave any resources for the host OS to manage the KVM emulation overhead. Things will likely be rather sluggish as a result. Better for performance to under provision rather than over provision.

You didn't leave any resources for the host OS to manage the KVM emulation overhead. Things will likely be rather sluggish as a result. Better for performance to under provision rather than over provision.

 

Indeed, I have considered that and I'll also experiment with it once the system is built.

unRAID numbers cores from 0.

Also, it's better to leave core 0 (and it's hyperthreaded clone) alone. unRAID overhead prefers to use core 0.

In your case, you probably have better performance assigning core 1+2 to VM1 and 3 to VM2; leaving core 0 for unRAID.

Another thread mentioned that core assignment means that a VM can only use the assigned cores, not the others. So now I'm thinking of assigning all cores to all VMs. Though I guess I'll just have to experiment with it and try to find the optimal configuration.

 

Good to know about unRAID and core 0, however. I'll take that into acocunt.