Gunfight at the ‘OK’ Corral: could you change hypervisors?

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In my article The Good, the Bad, and the Ugly I discussed the controversial licencing change which is coming with vSphere5. Many people are saying they’ll move to a competing hypervisor to escape these potentially higher license fees and even though my company aren’t facing this issue (our vRAM entitlement is sufficient in the short term at least) at some point my management team are going to (or should!) ask me to justify the expense and whether there are suitable alternatives. Most people I speak to acknowledge that the competition can’t compare with vSphere for features or maturity but they do discuss when they’ll be ‘good enough’ to satisfy the more basic requirements (and at a cheaper price?). So is now the time for the competition to shootdown vSphere?

‘Gunfight at the ‘OK?’ corral!

I needed facts so I set out to see how feasible a change would be and if the benefits were justified. For the purposes of this article I’m going to concentrate on the three main virtualisation vendors recognised as leaders by Gartner – VMware (vSphere), Citrix(XenServer) and Microsoft (Hyper-V). I’m also going to focus purely on my own environment – I don’t know XenServer or Hyper-V well enough to do a general purpose comparison and there are too many factors to consider in a single blogpost.
PS. If you’re after a general comparison  I’d suggest starting with Andreas Groth’s virtualisation matrix. This excellent site lets you see at a glance the feature sets of the three main hypervisors and even generate custom reports. Note that the site starts with the free version of ESXi and XenServer selected for comparison. You can use the menus on the left to change the version for each solution etc as required – nice!

Before even worrying about general performance, stability, quality of support, roadmaps etc I thought I’d do a feature check specific to my environment. We’re primarily using our VMware platform for server consolidation – we’ve done the P2V game for all but a few tier1 apps and now use it heavily for dev and test environments which are 100% virtual. As an Enterprise (not Enterprise+) licencee we don’t have access to some of the higher end features (distributed switches, host profiles, SIOC) nor are we using the extended VMware ecosystem such as SRM, Cloud Director, Orchestrator etc. Given our relatively simple use of virtualisation I suspected we’d be a good candidate for the ‘good enough’ competitors.  Comparing vSphere Enterprise vs Hyper-V Enterprise vs XenSever Enterprise Edition I found that;

  • We use storage vMotion all the time to rearrange our underlying storage for capacity or performance reasons, or to migrate to new Netapp arrays etc. Moving to a rival hypervisor would mean losing this functionality as neither XenServer of Hyper-V offer a completely nondisruptive migration. Given the downtime this would cause the business it would either result in lots of out of hours work (with associated overtime costs) or disruption to the business – both of which I know they’d rather pay more to avoid.
  • Alongside various flavours of Windows we run a significant number of Oracle Enterprise Linux  and Red Hat Enterprise Linux servers. When I last looked back in early 2010 Hyper-V only supported a single vCPU for Linux VMs and while it now supports vSMP (up to 4, same as our Enterprise licence of vSphere) only RHEL and SUSE are officially supported. A quick Google shows that OEL does work but that’s another argument altogether. Xenserver supports both online pharmacy no rx RHEL and Oracle Enterprise Linux (v4 and v5, both of which we use).
  • We use plenty of VLANs on our ESX blades (HP C class) which Hyper-V would work with but XenServer would not. It requires management ports to be ‘access ports’ and in blades with limited pNICs we’d have a problem. We could work around it using HPs Virtual Connect, Xsigo etc but that’s more cost and complexity.
  • We currently use NFS for the majority of our VMware estate and while our underlying storage arrays offer both FC and iSCSI (and we have a SAN fabric in place) it’s not a change we’d make lightly. XenServer supports NFS but Hyper-V does not. We have inhouse expertise on other protocols but it means changing our processes, provisioning scripts, documentation, training etc. It’s also a significant technical change so would consume quite a lot of time in change requests and implementation. Management would want to clearly justify the time and risks involved.
  • We currently get nearly 50% memory overcommit on our ESX hosts, a feature which saves us money on hardware purchases and isn’t available in either competing hypervisor. Hyper-V does offer Dynamic Memory but it doesn’t work with Linux VMs, which rules it out for us. With vSphere5 and the new vRAM licensing this benefit is largely lost however.
  • We’ve used Update Manager to a significant degree and while Hyper-V offers similar functionality via WSUS (which we already have deployed), XenServer is more limited.


For my specific circumstances the competition is not ‘OK’ because we’d lose functionality we rely on.

This will vary for everyone and will be completely different if you’re just starting down the virtualisation road and don’t have a feature-set to match up to (in which case this VMware vs XenServer cost calculator or VMware vs Hyper-V cost comparison might help). Could we work around all the issues above? Sure we could, but would it be cost effective? Having already paid for our VMware licensing we aren’t going to simply drop the technology however, at best we’d add new capacity using an alternative hypervisor and slowly migrate all hosts to the new platform. If we did go down that road then we’d have the challenge of running a multi-hypervisor infrastructure at least in the short term – increased training, increased complexity, limited toolsets (most support a single hypervisor only), interoperability issues etc.

The whole reason behind this research was to see if we could save money, and if that in turn justified a switch. This is always tricky as it’s rarely an ‘apples to apples’ comparison but my brief findings were that any cost saving would be eaten up by new toolsets, training, migration costs etc. I’d also note that as we’re entitled to vSphere5’s new features for no extra cost the competition is going to have to improve futher still to make this change feasible in the future.

If the recent licensing change means your costs will increase or you just want to reduce vendor lock in I’d recommend doing the same comparison for your infrastructure to see how feasible a change really is. I suspect VMware are able to raise prices (even if only for the alleged minority) because they know that for most people it’s not a viable or particularly attractive option.

Further reading

Is Hyper-V good enough?

This free online training from Microsoft Virtual Academy is a good place to learn more about Hyper-V.

Xenserver and Hyper-V make the ‘leaders’ quadrant

Why VMware continues to dominate despite Hyper-V advances

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