Virtualization shoot-out: Understanding the spread
Although VMware still leads the pack in features, not all of them carry the same weight when placed in any given corporate environment. Three features that will matter to environments of any size are live VM migrations, high availability, and load balancing.
Live migrations are the ability to move running virtual machines from host to host without rebooting. High availability allows a solution to determine when a physical host is down and automatically restart the virtual machines that were running on that host elsewhere in the farm. Automated workload balancing levels the VM load across multiple farm servers based on thresholds set by administrators. These are key features that once were available only from VMware, but are now present in each solution.
Following those features are slightly less important ones such as thin provisioning, VM snapshotting and templating, automated VM backups, live storage migrations, and advanced memory management features, including page sharing, memory compression, and memory ballooning.
VMware is still the only solution that can handle live storage migrations, and only VMware vSphere and Red Hat Enterprise Virtualization can claim to offer page sharing and memory compression. However, the other features are available across the board. Thin provisioning and templating are features that make deploying large numbers of VMs trivial, and at the same time reduce the impact on storage. Advanced memory management capabilities optimize the allocation of physical memory to virtual machines.
These tools are extremely important in infrastructures running a large number of VMs per host, and a large number of VMs overall, but smaller environments may not need them straight away. While definitely important, these features do not have as direct an impact on end-users as live migrations, high availability, and load balancing, especially considering the number of smaller organizations that are planning on virtualizing their entire server farm and will experience less churn than larger infrastructures.
Further down the feature trail, we get into more rarified air -- and items like API integration, which can provide massive benefits to larger implementations. All four solutions offer some form of CLI or scripted management, ranging from VMware's mature API integration to Hyper-V's use of PowerShell to allow for scripting administrative tasks.
There's also something to be said for guest OS support. Only VMware goes as far as explicitly supporting Mac OS X Server, FreeBSD, NetWare, and Solaris. You can even run OS/2 Warp if you like. The rest stop at a few Linux distributions and Windows platforms.
The long and the short of it is that at this point in time, all of these vendors can provide enough features to consider their use in a production capacity in a wide variety of deployment sizes and types. However, VMware still has the most mature and feature-rich offering among them. You'll find a features comparison table on the next page; the article continues on the following page.