Free memory is smaller than installed memory

[Getfeus]

Hello. I am using VSphere 6 with X99 chipset Intel system.

In my system, memory can installed up to 4 dimm.

First, I install 2 dimm of 4GB memories and vsphere client's  memory configuration menu shows that installed memory is 8GB.

But, I can't create VM over than 4GB. I don't know why but In resource allocation of my host said that, free memory is only 4511MB.(Still, configuration -> memory show 8GB)

So, I install new 4GB memory to my system and free memory at configuration -> memory shows new total memory is 12213MB. But, at resource allocation shows that, only 8406MB is available.

I want to know 'how can I use all free memory'?

Is this represent, one of my dimm is OOW?

Thank you very much.

[a_p_]

Welcome to the Community,

That's expected. The "missing" memory is required by the host OS (ESXi) itself.

André

[Getfeus]

Can I adjust memory reserved by ESXi itself?

4GB is too bigger for my memory.

For example, Xen can adjust Dom0 memory.

Thanks you for your answer.

[a_p_]

I'm not aware of a way to reduce the memory footprint of an ESXi host. The documented minimum requirement for ESXi 6.0 is 4GB, and from my tests (as well as several posts here in the communities) it doesn't even install with less memory.

André

[JarryG]

"...That's expected. The "missing" memory is required by the host OS (ESXi) itself..."

~3.5GB required for ESXi??? I supposed ESXi to be light-weight hypervisor...

BTW I have 32GB ram in my server, out of it 31GB assigned for VMs, 100% reservation, all runninng, and still have ~300MB free (ESXi 5.0)...

[a_p_]

Unfortunately, I can't tell you which new features require the memory.

However, from vSphere 6.0 Documentation Center

ESXi requires a minimum of 4GB of physical RAM. It is recommended to provide at least 8 GB of RAM to run virtual machines in typical production environments.

André

[RichardBush]

Hey,

I just span up a Esxi 6 lab to check this, if I assign 4gb to the host, once its booted its using around 1.5 gb, leaving 2.5 free. So id say 3.5 GB is a lot for the hyper visor to be using.

I was also able to start a vm with a 4gb memory assignment.

[RichardBush]

What does OOW mean ?

Have you tried switching them to see if a configuration gives you 8GB with 8GB (- the hypervisor overhead ) usable ? Maybe you have a DIMM that's not being used for some reason.

R