"And how would you like to pay for that?" It's a question that you're probably asked many times a week as you go about purchasing everyday necessities.
When it comes to server virtualization, you also have a choice of ways to pay. The problem is that the choice isn't between cash or credit card; it's between diverse pricing structures based on servers, processors, VM usage (indirectly, through vRAM usage), bundled guest OS licenses and arcane and unhealthy combinations of these. That makes direct price comparisons and cost projections almost impossible. And we all know that when the amount of money changing hands becomes murky, it's the customer that suffers. Server virtualization technology isn't so hard to understand, but how can you choose the right hypervisor and the right virtualization technologies when you don't know what each one would cost you?
If you're interested in VMware, you'll have to get your head round the company's absurdly Byzantine pricing system, which basically sees you paying a per-processor fee for running vSphere 5 software, with an indirect limit on the number of VMs you can run. That limit is imposed through vRAM entitlements--the amount of virtual RAM (vRAM) that can be in use in running VMs at any one time. If you run out of vRAM entitlements and you want to run more (or more vRAM-hungry) VMs, you can't--unless you fork out for more licenses. Following a backlash when the company first introduced this processor plus vRAM entitlements pricing system, the company revised its pricing by making it more complicated than ever. VMs with more than 96GB of vRAM use only 96GB of vRAM entitlements, and vRAM usage is calculated on a 12-month average usage basis.
What about Microsoft's Hyper-V? Server virtualization isn't Microsoft's main raison d'etre, and that means the company is more concerned about selling Windows Server 2008 R2, which comes with Hyper-V. The Standard and Enterprise editions are licensed on a per-server basis, while the Datacenter addition is licensed on a per-processor basis. You can run one additional instance of the server software in the Standard edition, four in the Enterprise edition, and an unlimited number in the Datacenter edition, at no extra cost. And of course you can run any number of other supported guests, as long as you comply with the licensing terms for those OSes--up to the limits of the server--or Hyper-V's 384 VM limit, whichever comes first.
Microsoft's server virtualization pricing structure is certainly simpler than VMware's, because with Hyper-V you're not limited in your use of vRAM--but you must know how many Windows Server VMs you're likely to need, both now and going forward. The two base editions don't allow high rates of server consolidation, but the data center edition certainly does. Things are simpler if you don't want to virtualize Windows guests.
Enterprise Virtualization for Server Pricing
When it comes to Red Hat's Enterprise Virtualization for Servers, using the KVM hypervisor, pricing is done on a per-socket-based annual subscription. You can run as many VMs as you want, subject, of course, to any OS licensing requirements. But when it comes to planning for the future, a more powerful multisocket server to achieve higher consolidation rates means more subscription fees.
Citrix's XenServer is about as simple as can be. Forget about vRAM, and forget about processors. There's a rather handy free version, or you can pick up the more feature rich Advanced, Enterprise or Platinum editions for $1,000, $2,500 or $5,000, respectively. That's per server, and that's it. Even if each server is packed with RAM and multiple multi-core processors, the price is the same. There's no penalty if you want to run more or bigger VMs in the future on a beefed-up server with the same license.
In an ideal world, all server virtualization systems would be priced like this. That way you'd have meaningful price comparison, no cost constraints on achievable consolidation rates and a sensible basis on which to plan for future license purchases. Is that too much to ask?
Paul Rubens is a journalist based in Marlow on Thames, England. He has been programming, tinkering and generally sitting in front of computer screens since his first encounter with a DEC PDP-11 in 1979.