I/O bottlenecks in virtual environments are one of those facts of life that you'll have to get used to as the number of virtual machines starts to proliferate on your network.
And while there's no shortage of I/O virtualization technologies ready to speed things up, the fact is that traffic jams are likely to occur as much in storage as on the network. It turns out that the old bug-a-boo, disk fragmentation, is much more prevalent in virtual environments than in physical ones.
As this article from Bruce Boyers points out, the virtual machine sees the hard drive partition as its own dedicated disk drive. But in reality, the drive is storing data the way it always has: fragmenting files across the entire disk. When the VM sends out a file request and gets back only a fragment, guess what? Another request is sent out, and then another and another until the entire file is retrieved. Now multiply that by a hundred VMs or so, and you begin to see how traffic can slow down even with the most state-of-the-art network architecture.
The answer to this problem is obvious: defragementation. Unfortunately, the level of defrag that you're used to on your everyday server won't cut it in the virtual world. Even automated once-a-day defragementation won't be able to keep up, which is why the newest systems are being optimized for virtual service through continual background defrag. The trick is to use otherwise idle resources to continuously scrub the disks and keep data files in some semblance of order.
This is a tall order, of course, because it means disks are practically in constant motion, which introduces heat and power issues. It also has to function well even during periods of high activity when the drive is busy processing all of those requests. Of course, if the disks are kept relatively clean, then the number of requests should go down, and everybody's happy.
Both VMware and Microsoft are turning to third-party solutions to keep fragmentation at bay in their respective platforms. Two companies, Diskeeper Corp. and Raxco Software, were among the first to gain Hyper-V certification under Windows Server 2008. And both have close ties to VMware with bundled or integrated solutions on the way.
Both systems rely on proprietary technology to smooth things out on the storage level. The Diskeeper 2008 relies on a proprietary technology called InvisiTasking that provides transparent defrag even if a disk is 99 percent full. Raxco PerfectDisk 2008 uses the company's Space Restoration Technology to provide free-space consolidation in virtual environments and SmartPlacement optimization tools for improved data flow.
Defrag may not be the first thing you think of when it comes to optimizing virtual networks, but it does provide a more orderly foundation that can greatly simplify matters for higher-level I/O processing.