Unable to hot-add memory to VM

Products

• VMware vCenter Server

Issue/Introduction

Typically this can happen when you try to add a small amount of memory to a VM. Addition of larger amounts of memory can complete without issue.

hostd.log contains the following:

Reconfigure failed: N3Vim5Fault20GenericVmConfigFault9ExceptionE(Fault cause: vim.fault.GenericVmConfigFault

 

vpxa.log contains:

--> (vim.fault.GenericVmConfigFault)

...

-->          message = "Unknown error."

 

vmware.log for the VM contains the following:

vmx - memoryHotplug: Change of memory size from XXXXX to YYYYY was requested

vmx - memoryHotplug: Please increase guest size to at least ZZZZZZMB to trigger hotplug event

 

Environment

vCenter Server 7.0

vCenter Server 8.0

ESXi 7.0

ESXi 8.0

Cause

This is expected behaviour.

Resolution

To determine the minimum amount of memory required to be added, perform the following steps:

Determine the Vmid of the VM:

vim-cmd vmsvc/getallvms

Using the Vmid from the previous output, execute the following:

vim-cmd vmsvc/get.config <Vmid> | grep hotPlugMemoryIncrementSize

For example,  If memory is 200 GB and being increased to 208 GB. wherein the hotPlugMemoryIncrementSize value is 8182. The task would fail with unknown error 

200 GB * 1024 =204800 

208 GB * 1024 =212992

204800-212992 = 8192 

The value should be greater than the hotPlugMemoryIncrementSize