VMware Server is a best-in-class hosted virtualization solution and provides an ideal way for new users to start using virtualization. It also works well for small deployments as well as application test and development. Potential VMware users often ask how VMware Server differs from VMware's ESX Server, our hypervisor-based virtualization solution. A complete response to that question would include long discourses on ESX Server's superior feature set, manageability, and overall reliability and robustness. Since I am hardly qualified to attempt such a thorough description, I'm going to stick with what I know - performance. At my VMworld 2006 talk, I presented a performance comparison between ESX Server and VMware Server using VMmark about which I am often asked. We ran VMmark using ESX Server on an HP DL585 with four 2.2GHz dual-core processors. We then ran VMmark on VMware Server using a similar HP DL585 with four 2.4 GHz dual-core processors. The results slide from that talk is shown below. (Thanks to my colleague Lisa Roderick in our Cambridge office for collecting the VMware Server numbers.)
These results show that ESX Server not only achieves higher throughput than VMware Server for a single VMmark tile (6 workload VMs) but also exhibits better scalability when a second tile is added. This behavior is a natural consequence of the different virtualization approaches taken by the two products. VMware Server runs on top of a heavyweight, general-purpose host operating system, which manages the hardware resources. (The host OS was Windows 2003 Server in these experiments.) On the other hand, ESX Server manages the hardware resources directly and is highly tuned to efficiently support virtual machines. This optimized design reduces the overhead for individual VMs and produces higher benchmark throughput in general. It is also unsurprising that ESX Server's highly tuned VM resource management provides superior scalability as more workloads are run.