I have been using VMware ESX server for about 3 years so I am unlikely to change products due to the investment in both time and money. It is a great product, fully featured, mature, but expensive. I'm not saying that it isn't worth the money, but if budget is an issue it can be difficult to get all the features you need.
Citrix XenServer is based on the Open Source Xen Hypervisor. I don't know anything else about the Citrix product, but I have read very good things about VirtualIron (
) which is also based on Xen, and has been around a lot longer than the Citrix offering, as far as I am aware.
The advantage of Xen over VMware is that it can take advantage of the virtualisation technology built into modern processors. VMware however wrote their systems before the technology existed so they had to come up with their own method which I believe is called binary translation. This gives Xen a potential performance advantage.
Speed on its own is not really a reason to go with one product over another. Cost is obviously important, but you need to look at the features offered.
Does Citrix/VirtualIron offer the equivalent of Vmotion, HA or DRS? I don't know about Citrix, but VirtualIron appears to, and they are key selling points for VMware. Do they have as good a P2V tool as the Vmware Converter Enterprise product?
One consideration is that Xen appears to have a smaller pool of Guest operating systems supported. It doesn't appear to support NT, so if you have some older servers they will have to be upgraded.
I suggest you look at the options available in a mature product like VMware, and work out what features are likely to be of benefit to you now and in the near future. Then take a look at the other products, and see if they offer an equivalent. You only need the features if you intend to use them.
I would also consider what methods are available for backup purposes. Are there 3rd party products available if needed?
Additionally you may consider how easy it would be to get support on Xen apart from official sources. It took quite a while before there was any useful information on the Net about VMware.
I looked for a decent comparison article, but the only seemingly decent ones I could find were by the product makers, so I think you have to take their opinions with a pinch of salt.
Rik
