Virtualization shoot-out: VMware vSphere

Although the Citrix, Microsoft, and Red Hat solutions now offer live VM migrations, cloning and templating, and other significant features, VMware still goes well beyond them. Perhaps vSphere's most noteworthy advanced features is Fault Tolerance, which brings continuous availability to a VM by running primary and secondary versions across two hosts simultaneously. In testing, Fault Tolerance functioned quite well: Pulling a blade running the primary instance of a fault-tolerant, heavily loaded VM went unnoticed by the workload, which was suddenly happily ticking away on the secondary host without missing a beat. While this is certainly an impressive feat, the single-vCPU (virtual CPU) limit may preclude its use in many cases.

There's also Distributed Power Management, a companion to vSphere's Distributed Resource Scheduler that allows vCenter to consolidate VMs on fewer hosts during idle and off-peak hours, as well as dynamically power hosts off and on as the load on the farm changes. In a large farm, this feature can save significant power and cooling costs without any performance degradation.

VMware vSphere is also the only solution that can handle live storage migrations, where a VM disk can be shuffled between storage targets at will without disrupting normal operations. Neither XenServer nor RHEV have provisions for storage migrations, and though Hyper-V can move virtual machines between arrays, it needs to suspend the VM for a period of time to do so. With live VM disk migration, upgrading back-end storage behind a virtual server farm is no longer an all-night, downtime-laden affair, but a task you can do over coffee in the early afternoon.

In addition, there's VMware Data Recovery, which allows for fine-grained VM snapshot scheduling, backup, and recovery. VMware's capacity planning tool, vCenter CapacityIQ, monitors an existing vSphere farm and allows you to run what-if scenarios that can help increase the farm's efficiency. Beyond that, VMware's plug-in architecture supports features such as Update Manager, which can be used to maintain not just the vSphere host servers, but also the updates to the operating systems on the VM's themselves.

Then there are the additional features found in the high-end versions of vSphere. Storage I/O Control and Network I/O Control help even out the load on heavily tasked hosts, ensuring that when I/O resources become oversubscribed, the most important VMs vying for storage and network access get what they need. VMware vSphere also supports distributed virtual switching and the Cisco Nexus 1000V.

Other features go beyond the competition, such as the ability to hot-add CPU, RAM, and disk resources to VMs running compatible operating systems. Although other solutions can hot-add disk and perhaps network resources, only VMware can handle CPUs and RAM as well.