Free Hypervisors Comparison

I often read debates and opinions on the internet concerning the pros and cons of the free versions of the three most widely-spread hypervisors.

Here's my view on them:


ESXi:


Pros:

• It's the most popular bare-metal hypervisor, so whatever problem you encounter you can just google for the answer.  
• Supports a huge number of Guest OSes 

Cons:

• It's not free; this is not even a clever marketing technique. It's a bait and switch, plain and simple. Let me elaborate here. ESXi is free, which is the hypervisor part. Great. But its management tools aren't. So you can't do absolutely anything with it. If you want to actually install a guest OS, you'll need the vSphere client which costs thousands of dollars, or VMware workstation that you will need to use to connect to the ESXi remotely (a solution which will set you back a few hundred dollars instead). 

• I have found its command line to be obtuse. I know, eye of the beholder and all, but it would be much easier to learn if it had completion for its commands as well as the command parameters, just like XenServer.

Hyper-V:


Pros:

• If you're planning to install a Windows OS, look no further. Microsoft has done a great job with the optimization and performance of Windows-based VMs. 

 
Cons:

• Even though it is dead simple to actually install the hypervisor you can't do anything unless you have set up and configured users, domains, firewall rules, etc. from the command line. If you're not already familiar with PowerShell, this can be a daunting and time consuming task (actually, it is a time-consuming task even if you are familiar with the PowerShell). Luckily, there is a script out there that takes care of most of these tasks, reducing the time taken to actually set up everything. After that, you'll need to install the RSAT tools and Hyper-V tools on your PC. Finally, if you're running windows 8, for some strange reason, Microsoft has also decided that you will need the Pro Edition to manage your Hyper-V server.
• It does not provide zero-downtime live VM migration  
• Dynamic Memory is only supported with VMs running Windows Vista SP1 and above, or Windows Server 2008 SP2/2008R2 SP1, 2003 R2 SP2 and 2003 SP2.
• If you're planning to use Linux, you'll need to install the legacy network adapters, and after you're done with the installation of the Linux Integration Services, you'll need to substitute the network adapters for better ones; somewhat minor irritation, I know. 

XenServer:


Pros:

• It's a fully-fledged Operating System based on Red-Hat 5, which means you can tweak it and do whatever you want. For instance, you will need to have specialized software to take backups of your VMs if you're running Hyper-V or ESXi. You can if you want with XenServer, but personally I've just written a perl script. And it works great. And guess what, too: my backups are written to a GlusterFS volume. If I had ESXi, I would have to use the insecure and deprecated NFS protocol for that. On XenServer, I just had to install GlusterFS, like any other Linux node.

• Its command line is unbelievably good. And extremely easy to learn. You can do everything with it.

• The free version is not a watered-down version of the paid one. Almost anything you can do with the XenServer paid version you can with the XenServer free version, except features like GPU virtualization, in-memory read caching, support and patching (you'll have to patch using the command line if you're using the free version).

Cons:

• XenServer used to have a great networking management interface called the Distributed Virtual Switch Controller. Unfortunately, this tool became deprecated as soon as the product was decided to become open-source. Of course, since XenServer is a fully-fledged Linux distro, this means that it is trivial to actually solve any network-related issue by switching our networking stack to Linux bridge, and taking it from there.