Max memory to a VM when running single on a host?

[kb_sweden]

Hi,

I have a ESXi 4 host with 65522,60MB RAM as reported capacity.

I have one single VM RHEL 6 64-bit running on it.

It is possible to allocate 65524MB RAM to it, and I have done so.

Is this correct? I guess the host system needs some RAM too, and by allocating all RAM to a VM you may wonder where the host system gets its RAM from?

Everything is working, but I just wanted to clarify this, if anyone can help me bring some light over this?

[Troy_Clavell]

The guest will only use what it needs, so this is why you can provision and even oversubscribe memory.

[rickardnobel · Accepted solution]

Hej Kb,

you could in ESXi overcommit your memory, for example running 10 VMs with 8 GB of RAM on your specific host. ESXi has certain memory management techniques to handle the RAM as efficient as possible, however if all of your VMs (or in your case your single VM) would really need all RAM then it wont fit in physical RAM and has to be handled by some different ways, but could end up with so called vmkernel swapping = bad performance.

For your VM it is likely best to set it to something like 62 GB or similar, since this make the ESXi host operating system and your whole VM fit into RAM completely.

[weinstein5]

Welcome to the Community - short answer yes you can - as the other have mentioned ESXi memory management allows you to overcommitt memeory but I want to second that you should assign memory to what you really need -

[kb_sweden]

OK thank you all!

My goal is to get maximum performance for this single VM, so I gather setting max RAM to like 60GB as suggested will be the right amount for this.

[rickardnobel]

kb_sweden wrote:

My goal is to get maximum performance for this single VM, so I gather setting max RAM to like 60GB as suggested will be the right amount for this.

I think that would be wise. You still can't really use the last gigabytes for this VM and by that there is no real point of having the VM belive it could use that memory.

Lycka till.