For optimizing computer resources, for energy reduction and for lowering server footprints, server virtualization is the single most remarkable innovation to come along yet. How far we have advanced from the single-cabinet machines that drained costly power and required feet of space each. Virtualization is even a quantum leap over rack-mounted servers and server blades, as virtual machines literally take up no space at all and several require the energy previously needed to power one full machine.

With all the work now being compressed into one physical machine, however, performance is obviously a crucial element. If there are bottlenecks at any of the hardware junctures, it no longer affects one server, but several -- along with all their processes. Slow access times and reduced reliability then erode the substantial savings that virtual machines would normally provide.

At the root of virtual machine performance problems is file fragmentation. The key to understanding fragmentation's impact on virtualization lies within the word "virtual" itself. For storage, virtual machines are making use of hard drive partitions which appear as entire drives dedicated to the virtual machines. But underneath the "virtual" layer, the hardware is storing files the way it always has, utilizing an entire disk and fragmenting files from all partitions across the whole drive.

Virtual machines have their own I/O requests which are passed along to the host system. Hence, multiple I/O requests are occurring for each file request -- minimally, one request for the guest system, then another for the host system. But in a common fragmentation scenario, especially with virtual servers creating high amounts of disk activity, files will be fragmented in to tens, hundreds or even thousands of fragments. Imagine the frantic activity with multiple I/Os for each fragment of each and every file requested. As virtual machines (VMs) share a common hardware platform, excessive and unnecessary use of hardware/storage resources by one VM slows not only the requesting VM, but all other VMs on that platform.

Virtualization is advanced technology and requires a defragmentation technology that is comparably advanced. Because of today's high rates of fragmentation, and because many servers cannot be taken offline except in the severest of emergencies, scheduled defragmentation is no longer an answer. In addition to the impossibility of scheduling enough defrag runs, fragmentation continues to build in between what runs can be scheduled, heavily impacting performance and reliability.

The only real solution to optimizing virtual machine performance and reliability is a fully automatic defragmenter, one that is constantly taking care of the fragmentation problem. Using only otherwise-idle resources, such a solution operates in the background with no negative performance hit. Virtual performance is constantly maintained.

In evaluating any defrag solution for a virtualization platform, ensure that the defragmentation technology chosen will allow the full exploitation of virtualization's benefits.