Server 2016 hot add memory

[gknight_uob]

Hi all, I wondered if anyone could provide more info than VMware support.

We have a server 2016 VM (16 vCPU, currently 64GB memory), when trying to increase memory (hot add) to 80GB, it sets to only 76GB. If we try to set to 80GB again it fails. In the logs we receive:

2020-04-28T11:58:21.536Z| vmx| I125: memoryHotplug: Change of memory size from 77824 to 81920 was requested

2020-04-28T11:58:21.536Z| vmx| I125: memoryHotplug: Please increase guest size to at least 86016MB to trigger hotplug event

VMware support say this is a guest OS issue. Does anyone know why we can't increase to 80GB but could go to 86GB?

Any support will be greatly received

Thanks

Graham

[daphnissov]

If VMware support is saying it's a guest OS issue, you are probably better served taking it up with Microsoft.

[GregSmid]

Morning Graham, did you ever find a solution for this? I'm getting the same error on one of our VMs and having a hard time believing it has anything to do with the guest OS.

2020-12-08T21:34:45.740Z| vmx| I125: VigorTransportProcessClientPayload: opID=168bc7f4-01-26-f300 seq=1392383: Receiving Chipset.SetMemSize request.
2020-12-08T21:34:45.740Z| vmx| I125: memoryHotplug: Change of memory size from 34816 to 36864 was requested
2020-12-08T21:34:45.740Z| vmx| I125: memoryHotplug: Please increase guest size to at least 38912MB to trigger hotplug event
2020-12-08T21:34:45.740Z| vmx| I125: VigorTransport_ServerSendResponse opID=168bc7f4-01-26-f300 seq=1392383: Completed Chipset request with messages.

[vGuido]

Hey Greg,

did you ever find a solution for this? I'm getting the same error on one of our VMs.

[continuum]

Just think like a mainboard.

With 76 gb installed you want to add a 4 GB RAM module.

Divide 76 by 4 and get 19 as a result. Do you think any mainboard existing nature has 20 ram slots ?
If such a RAM change appears to be smaller than any real life operation the mainboard may not even register a change.

Use more natural steps like changing from 4 x 16gb to 5 x 16gb  - thats exactly what the original message suggested as well .... after all a mainboard is only human ...🤒

Ulli

[vGuido]

The problem is, that I wanted to upgrade from 128 to 192, which is not uncommon. For whatever reason, vSphere extended the memory only to 184 GB. And now I can only extend to 200GB. 

[GregSmid]

Hi vGuido,

I never really did find a good answer to this, other than to increase the memory to beyond the value listed in the logs. VMware Support said that they didn't know of any limitation in ESXi that could cause that, they suspected it was the guest OS passing that limitation back to the host... but couldn't tell me anything more than that.