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Eric’s post
[Updated below]
Eric Horschman over at our new VMware: Virtual Reality blog today writes about one way to evaluate the true cost of your hypervisor — and it’s not the sticker price. Leaving aside both functionality and operational costs, take a look at cost per virtual machine. Link: Cheap Hypervisors: A Fine Idea — If You Can Afford Them
VMware also has a great TCO/ROI calculator
to help you decide, but if all that seems like too much work, let me
propose a simpler metric for comparing hypervisors – cost per virtual
machine.Cost per VM is not that hard to measure: just add up the costs for
the server, the virtualization software, the operating systems and the
application software; then start adding VMs running your workloads
until they can no longer meet your required service levels. We’ve
actually done that work for you and you might find the results
surprising.
We took a common dual socket server with 4GB of RAM and tried the test
with ESX Server 3, Citrix XenServer v4 and Microsoft Hyper-V beta. We
created and powered on 512MB Windows XP VMs running a light workload
and kept adding them until the server couldn’t take any more. Our
Hyper-V and XenServer tests topped out at six and seven VMs
respectively, which was expected. You see, both those products subtract
the full amount of memory allocated to each running VM from the host’s
physical RAM. When you factor in the additional memory required by the
hypervisor and the management OS, there’s room left for at most seven
VMs. In fact, XenServer and Hyper-V will flat out refuse to let you
power on an additional VM with a warning that memory resources have
been exhausted, as shown in the screen shots below. XenServer and
Hyper-V can’t do what we call “overcommiting” memory and that should
strike you as tremendously wasteful when most data center VMs are
lightly utilized.
Eric goes on to explain VMware’s transparent page sharing and balloon memory driver that together allow ESX Server to get roughly double the number of VMs per server than other hypervisors that don’t have this technology.
Finally, we do the division and find that even our high-end VI3
Enterprise bundle beats a free hypervisor in cost per VM! Going with
any other hypervisor means you’ll need more hardware, network and
storage connections, switch ports, floor space, power and cooling to
support a given population of VMs. That should make your decision easy
if all you’re doing is simple server consolidation, but there’s more to
consider. VI3 Enterprise includes a powerful array of virtual
infrastructure services like VMotion, DRS, HA and more that let you
automate, optimize and protect your operations, and those features put
us far ahead of the offerings from the Xen vendors and Microsoft.
Update: Eric seems to have touched a nerve, so he’s going into more detail. Make sure you check out the comments on both posts — interesting discussion and real customers. Link: More on VMware Memory Overcommit, for Those Who Don’t Trust the Numbers | VMware: Virtual Reality.
More on VMware Memory Overcommit, for Those Who Don’t Trust the Numbers
James O’Neill of Microsoft had a pretty sharp reaction
to my post. He accused me of cooking the numbers to exaggerate the cost
saving benefits of VMware’s memory overcommit feature. To help James
understand just how memory overcommit works, I’ve taken the numbers out
of the argument and have used simple algebra to compare the TCO per VM
for a host with either VI3 or Microsoft hypervisors. Let’s do the math…