More than one year ago virtualization adopters looking for new Microsoft hypervisor, Hyper-V (at that time called codename Viridian), had great expectations because of one groundbreaking new feature in the work: the capability to add new virtual hardware (virtual CPUs, virtual RAM or virtual NICs) on the fly inside running virtual machines.
This feature alone was interesting enough to put some enterprise customers to refrain from jumping on the VMware bandwagon.
Unfortunately, in May 2007 Microsoft announced the drop of hot-add support from its roadmap, postponed to an unannounced date.
At that point was clear that Microsoft competitors could implement that feature earlier than Microsoft itself, since the capability to add new hardware live doesn’t depend on the virtualization platform itself, but rather on the operating system.
This depends on the Dynamic Hardware Partitioning (DHP) technology that Microsoft started to implement in Windows Server 2003 SP1 and which is fully enabled in Windows Server 2008.
And now, as supposed, VMware is the first to introduces the new hot-add support.
The information is hidden in the just published Workstation 6.5 beta 1 feature list:
New virtual hardware version — This new hardware version lets you use the following new features if the guest operating system supports them: Add or remove some virtual devices while the virtual machine is powered on (“hot-plug”). Use LSI Logic SAS (serial attached SCSI) adapters in the virtual machine. 3-D graphics capabilities are enabled by default. Hot-add virtual CPUs and memory to a Windows Server 2008 guest.
So while Microsoft is still struggling to release Hyper-V 1.0 (expected in August 2008) which will not support hot-add, VMware is already near the release time.
The well-known VMware software lifecycle implies that new features are first introduced in VMware Workstation and after a good time are slipped into ESX (formerly ESX Server). So we may not see virtual hardware hot-add support in upcoming ESX 3.5.x releases but ESX 4.0 may have good chances to implement it.