VMWare vs Citrix Xen Comparisons ....

I have used both products for long time and I can tell you that Citrix Xen has better virtualization strategy for any business size.

Let's make the point.

VMWARE Facts

•  it has been the longest time.
• They started offering VMware server for free however this product does not perform very well on production enviroments.
• After a while, They decided to offer ESXi version for free. It was a good move however ESXi does not have console access because they designed to be embedded. This means limited access and flexibility.
• VMware never allows public performance comparisons. This is very obvious, why a company would do that. Furthermore, they created their own performance benchmark. 
• VMware is a commercial product that requires license for everything. Call your sell rep and ask him about prices...Morevover VMWare needs to be careful with piracy. 
• VMware did not offer paravirtualization. If I remeber they started to offer paravirtulization recently. Paravirtualization gives a lot better performance than full-virtualization.
• VMware Virtual Center is sold separately and it only runs on windows. This product is required to perform most of the advantage of the virtualization.

Citrix Xen Facts

• Although it is pretty new product, the Xen Hypervisor has been around for a while.
• First people must distinguish between Citrix Xen and Xen. Citrix Xen is a whole suite that uses Xen. Xen is the free hypervisor built by Linux Community. You can use Citrix Xen or Xen separately.
• Initially, Citrix Xen was not free, because Citrix felt very confident about this product however VMware had basically most of the market. The market was reluctant to change to the new platform so Citrix offer was not too attractive.  Finally they decided to offer Citrix Xen 5 for free with all the features.
• Citrix Xen is commercial product based on Xen Opensurce. Citrix Xen Server is free with all features. If you want to go further you can add more features buying the Essential license or Platinun license.
• Citrix Xen has always offered paravirtualization. Paravirtualization was the core of Xen hypervisor.
• Citrix Xen Console ( vs VMware VC) is a client that connects directly to the pool of Citrix Xen Servers. It does not require a dedicated server.

Both products can offer you the same functionalities, however Do we use all those functionalities?

Let 's review what we need.

Required options:

• Storage Support (ISCSI, local storage,NFS)
• Cloning and Snapshot Capabilities.
• Guest OS support.
  
• Vmotion or Xenmotion capabilities. 
• Virtual switches support (multiple VLANs)
• Good Performance (Paravirtualization)
• Centralized console (Virtual Center or Citrix Xen console)
• Templates support.

Optional requirements.
These are options good to have however I have not seen people using them a lot. In addition, they can be provision in other ways.

• HA  and DR
  
• Specialized Storage support
• Automatic Load Balancing 
• Fast Provisioning

Now it is almost clear. If I have Citrix Xen 5 or 5.5 free I can provide all the required options, if I want to get the Optional requirements , I would have to pay or I can deploy different solutions. In VMware world, I can use ESXi for free however I am going to require to buy Virtual Center so I can manage all those servers. Moreover, I will require a windows license to install VC.

In Conclusion, both products are great, however I think that Citrix Xen can offer you more free so your learning curve and testing enviroment can be more productive.