I have an ESXI 6.0 with 8GB Ram. For some reason I can only use 4.7GB for VMs. I tried using esxtop but didnt see anything using lots of RAM. Below are screenshots from vsphere. Can anyone help me to understand where is Memory going? As you can below there is total 8104 MB RAM available but somehow 5.9GB is consumed. If I go to Resource allocation page, I only have 4.7GB ram to use for VMs.


Physical Memory

Available Memory

Consumed Memory

  • Are you using resource pools? – Chopper3 Nov 4 '15 at 18:21
  • I ****ing HATE resource pools, for 99% of users there's little benefit of using them and they can create a few pitfalls. Get rid of them and see how you get on. – Chopper3 Nov 4 '15 at 18:25
  • @Chopper3 My bad. I am not using resource pools. I am using standard Shares that came preconfigured with default esxi installation. I turned off both VMs and my ram usage was 1.4GB. Which is reasonable, however my available RAM for VMs was still 4.7GB. – Iuri G. Nov 4 '15 at 18:38
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    That's just not right though, I looked at one of my hosts and I was losing hundreds of MB not GBs and this is on a host with 768GB of RAM, it's definitely not right. – Chopper3 Nov 4 '15 at 19:14

Some RAM along with vCPU is used as an overhead reserve for the OS, this is normal. Think of it as a pagefile to Windows. As you add more VM's, that reserve might grow depending on your usage.

As this is a common thing, you most times see vSphere machines using extensive motherboards that come with numerous RAM slots and multiple CPU mounts.

The only real way to get around this unfortunately is to add more RAM if your motherboard can handle it. :)

  • I would expect maybe up to 1GB RAM reserved. 3.3GB sounds excessive. Even when I power down VMs, it is still same. I've read similar posts, and no one is having more than 1.5GB reserved. Does 3.3GB sound right to you? how much is there reserved on yours? – Iuri G. Nov 4 '15 at 18:21
  • To be honest, I have not used ESXI 6 yet, so things might have changed, I honestly don't know. But I have seen in ours and other environments up towards 5GB being reserved. The newest ESXI version might need a bigger reserve than it's predecessors, I'm not sure. – Jonas Lear Nov 4 '15 at 18:24
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    No not at all, that's still very odd, I wouldn't expect anything like that much memory to be used by the kernel. It looks like your server's very far from the HCL specs (I think) - I'm hoping that's got nothing to do with it. – Chopper3 Nov 4 '15 at 18:24
  • @Chopper3 - I was able to install from ESXI iso without modifications, so even though it is not certified hardware, I would not expect memory leak or overuse from it. I thought maybe part of RAM is not visible to kernel, but configuration shows that it is using all 8GBs. – Iuri G. Nov 4 '15 at 18:27
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    One word of gentle warning luri - serverfault is a site for professional sysadmins who like to build and run supportable systems in a pro-environment. I'm thinking this looks like a laptop you're running on right? in which case perhaps in the future you could consider asking questions about dev/test setups like this on our sister site superuser.com as they cater better for this kind of system ok. – Chopper3 Nov 4 '15 at 18:31

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