Cost Per VM more important that cost of Hypervisor:


http://blogs.vmware.com/virtualreality/ has a good case study comparing the major advantage VMware has over the compeition with it's memory technology. The # of vms you can run and cost savings are amazing! I will summarize below but please read the full story at the link above.

- 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.

-The VMware ESX Results (ESX=40 vms, Hyper-v=6, XenServer=7)

-Those 40 VMs have more than 20GB of total RAM allocated and they are running fine on a server with 4GB of physical RAM – a 5:1 memory overcommit ratio. Our exclusive ability to efficiently overcommit memory lets VMware Infrastructure support more than five times as many VMs on the same hardware as our competition! We repeated the test using Windows 2000 Server VMs running SQLIOSim to see how we fared with heavily loaded VMs. Hyper-V and XenServer both topped out at six and seven VMs again when they hit their memory limits, but the ESX Server platform ran fine with 14 VMs – twice as much as the other hypervisors!

-Now, let’s get back to the cost per VM comparison to see which hypervisors provide the most bang for the buck. In the table below, we add up the costs for a basic hypervisor deployment. We’ll assume a 2-way, 4GB server costs us $6,000. Next, we add the costs to run Windows in each VM. For that, we’ll take advantage of Microsoft’s policy that lets us run an unlimited number of Windows VMs on a host licensed with Windows Server Data Center Edition (and yes, that policy also applies to VMware and Xen hosts.) Licensing Windows Server Data Center Edition costs us $5998 for two sockets. After that, we plug in the cost of the VMware Infrastructure 3 licenses, and to make things interesting, we’ll assume the competing hypervisor is absolutely free.

-The next row in the table shows how many concurrent 512MB VMs each hypervisor can support. For VI3, we’re assuming a conservative 2:1 memory overcommit ratio based on our heavy workload test, which lets us run 14 VMs. For our hypothetical free hypervisor, we’re stuck at seven VMs because memory overcommit isn’t an option. That’s right, no other hypervisor technology allows memory overcommitment – it’s a VMware exclusive.

-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.

-If you’re ready to get started consolidating your servers, don’t be lured by seemingly low cost hypervisors into a decision that will limit your VM density and lock you into spending more on hardware. Instead, put memory overcommitment at the top of your list of hypervisor feature requirements. You’ll spend less on the project by stretching your hardware further and, since only VMware has memory overcommitment, you’ll get the proven reliability and advanced virtualization features of VMware Infrastructure thrown in for free. Beware the high cost of a “free” hypervisor.