On Virtualization

Surely, most folks in IT have heard about the tendency of virtualizing servers in order to save rack space, create an additional level of High Availability, and simplify the management of servers. I've jumped on the bandwagon a while ago, but have been careful enough to first virtualize the least critical servers and see how they perform in the long term, before even thinking about virtualizing the high-load production servers.

In my case, the perfect candidates for wide-stage production server virtualization were Terminal Servers, for the following reasons: The load on them is highly predictable, they are mostly memory-bound if there is a restriction on # of logged on users, and most importantly they are farm animals. The latter means that if there are any problems with the virtual servers, we can always go back to the idle physical ones, assuming we haven't already pulled them out of the datacenter.

There was an excellent study published by the LoginVSI project showing that terminal servers scale almost linearly in a virtual world, and figures such as 300 active users per dual quad-core physical host with enough RAM are very realistic and achievable.

Currently, there are 3 enterprise-ready vendors that can be used in a large-scale virtualization project: VMware, Citrix and Microsoft. They all have their benefits and drawbacks, but for the purpose of this project, due to various reasons that I might explain in another article, I chose Citrix XenServer 5.5 w/ Essentials.

My thoughts on XenServer so far: the technology is great, but support from the vendor takes way too long, if the issue is anything but primitive. Oh well, more in the next article.