VMware VI3, Microsoft Virtual Server, XenSource XenServer, Virtual Iron, etc… — Living Together in Harmony
Do you know how there are some questions that at first glance seem like they may generate long and complicated answers? Recently I was pinged with such a question, but then I came to realize that the my original answer, and in fact the question itself were both over thinking the situation. The question is, “What problems are there with running various virtualization solutions in the same data center?”
The answer is simple — there really are not any problems that do not already exist in any given data center that employs heterogeneous technologies. For example, there are the problems of redundancy, vendor support, free storage space, and staff expertise.
Imagine a data center that runs both Apache and IIS web servers. There are 2 Apache servers and 2 IIS web servers — the Apache servers run PHP applications and the IIS servers run ASP.NET applications. What happens if either all of the Apache servers go down or all of the IIS servers go down. Because all 4 servers do not use the same web server and the web applications are not based on the same language, the odds of quickly and successfully moving the load of the 2 downed servers to the other 2 are slim.
The same goes for a data center that implements various virtualization technologies. For every different technology employed, you potentially lose a little bit of redundancy.
In a given data center imagine there are Dell servers, HP servers, and IBM servers. That means 3 different vendors (unless you went through a VAR) for supporting your infrastructure. The same is true for virtualization software — having multiple virtualization solutions means having different vendors to contact when problems occur.
Free Storage Space
Available storage space is usually scarce in any data center. There is almost always someone or some system clamoring for more spindles. Throwing additional virtualization solutions into a single data center results in additional servers trying to grab whatever free space they can off of your storage device(s). Since most virtualization solutions use different file system types — NTFS, VMFS-3, ext3, etc…, different virtualization solutions cannot efficiently make use of other virtualization solutions’ free space. There are of course loop holes, such as mounting other file systems as a network file system, but these solutions result in a degradation of speed and also incur the overhead of a file system on top of a file system.
Implementing multiple virtualization solutions also means that your staff must now be experts on each piece of software used. This expectation is most likely unrealistic and can result in system administrators that are proficient in many areas but are experts in none.
While there are no technical reasons you cannot utilize virtualization solutions from multiple vendors in one data center, there are many reasons why it makes sense to stick to one vendor. However, there are always exceptions. The trick is to simply be mindful of the pros and cons in using heterogeneous technologies and to make the decision that makes the most sense for your environment.