What's in a Hypervisor
I think we're getting some terms mixed up here. Yes, the
Hyper-V hypervisor is 1 MB. vmkernel (the VMware
hypervisor) is also 1 MB (about 64 k if memory serves
me right). A hypervisor alone doesn't do you any good -
you need some way to get I/O through the box. The
hypervisor is basically a glorified traffic cop of sorts. I'm
oversimplifying but that's pretty much all it does -
schedule VMs and allow for the hardware abstraction.
In order to get I/O through you need some real drivers. In
Hyper-V they use the real Windows drivers in the parent
partition (Windows Server 2008 full or core). In VMware
the drivers are baked into ESX or ESXi. This is where the
real size difference comes into play
Also note there are 2 flavors of ESXi - embedded (for the
OEMs) and installable. ESXi embedded is about 32 MB. It's
small because it only needs one set of drivers for the
hardware it's going to run on. ESXi installable (the one
you're downloading from the website) includes a much
larger set of drivers since it can be loaded on any number
of servers. That's the main reason for the size difference
in the ESXi versions.
In Hyper-V you need that parent partition hanging around
for the drivers amongst other things. With a server core
(the light version of Windows) install it's about 3 GB. With
a full Windows 2008 install it's over 6 GB.
So with the newfound knowledge what's being compared
is 32MB for ESXi embedded or about 200 MB for ESXi
installable versus 3 GB for Hyper-V with Server Core or
over 6 GB for Hyper-V with full Windows.
Notice that the hypervisor really doesn't play into all of
this talk at all since it's pretty much a wash either way.
What does this size difference mean anyways? Basically it
means that with ESXi you get only the code necessary to
run VMs and that's it. With Hyper-V you get the code to
run VMs plus you have to drag along Windows in order to
make it all run. I don't even want to open the can of
worms on Windows security at this point but you can see
where the argument can go.
