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Understanding hot-add and hot-plug in Vmware vSphere

The hot-add and hot-plug of resources are very useful feature in vSphere where you can pile in more compute resources on the fly without a downtime for machines.Few points about this feature

  • "Hot-add" refers to adding more memory to a VM whereas "Hot-plug" refers to adding a virtual CPU to a VM
  • Inorder to change the hot-add/hot-plug status of a VM , the machine should be powered off i e if the feature is disabled, you should first shutdown the machine before you can enable it. This is enabled from VM settings-> options-> advanced->memory/cpu hotplug
  • The feature is not enabled by default
  • Minimum VM hardware version of 7 is required for hot-add/hot-plug to work. If you are using a lower version of virtual hardware, first you need to upgrade it
  • Even if it hot add/plug enabled, for the hot add/plug to be effective, it should be supported by the VM guest operating system for the resources to be available to the VM
  • Hot add/plug feature is not compatible with VMware FT
  •  Feature is available only on Advanced, Enterprise and Enterprise plus versions of vSphere
  • Hot "remove" of memory and cpu is not supported by vSphere, no matter what the guest OS is

Note: Supporting OS for hot add/plug feature

  •  Windows server 2003 Enterprise (x64 and x86 ), Windows server 2008 Std, Ent and datacenter editions support memory hot add. 
  • Windows server 2003 Std x64 and Windows server 2008 Ent x64 editions support CPU hot-plug
  • Linux OS supports hot add of memory but not hot-plug of CPU


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