I received today an email asking if I ever found a good paper comparing both products. I was answering, then thought that someone else could have same question so I prefer to post here my opinion about this:
I think a GSX vs ESX performances comparison article would never exist.
They are not only different products laying on different hardware handlers (operating systems as we like to call them).
The most important fact is that they handle system resources in a total different way: GSX follows standard allocation resources rules (in other words acts like a standard application) while ESX reallocates memory and CPU when needed among VMs.
This implies that ESX requires much less base memory to run, and a small footprint custom kernel helps this more and more.
Another important implication is that, IMHO, running a performant GSX server is much more difficult than running a performant ESX server: in GSX there are so much factors linked to OS and applications handling that could negatively impact on VMs performances. Perfectly knowing how to light and speed up your hostOS is THE task before any other optimization you can do on GSX itself. The study of the best hostOS (between Windows and Linux many variants) would merit so many pages.
In ESX everything is in VMware engineers hands. Yes, you can hack some small aspect but the gain doesn’t do the difference. In a sense you have no choice, so there are less probabilities to go wrong.
If you look at GSX vs ESX in a how-many-features sense, then is simple: GSX is unbeatable, and 3.0 edition will demostrate this at the best.
I’m a big fan of GSX and always suggest it to my customers for many reason: first of all I don’t like “appliance phylosophy” where you haven’t full control on underlaying software, then ’cause today, with Windows 2003 hostOS, I can achieve tasks hard to achieve with Linux hostOS or ESX.
But I perfectly realize that ESX performances are superior, and less prone to negative events.
Both GSX and ESX are going to raise level to same features pool, and you will notice better within some weeks. Probably ESX will insist on performances and super enterprise features (multiprocessor support, native SAN support, VMs fail over and load balancing, and so on), while GSX will insist on flexibility in any scenario (I expect a further improvement about this aspect when virtual driver SDK will be released).
An interesting move could be abandon Linux in future ESX versions and rebuild the product on FreeBSD, achieving superior network performances and stability, remaining with Windows and Linux for GSX versions. But I’m not a VMware engineer and maybe they already tried without good results.
Or, simpler, BSD wasn’t the best choice for the business.