Fast and mean virtual machines

One question mark always hanging over virtual servers is I/O performance. Unless the underlying OS and file system are specifically designed to handle a virtualization load, disk I/O can be problematic. With products like VMware ESX 3, the I/O subsystem drivers are tuned to a virtualization load, handling the widely disparate requests faster and more fluidly than the stock subsystem found in Windows Server and most Linux distributions. This isn’t a fault of these operating systems or their file systems, it’s simply a facet of the virtualization picture: A VM load is far different than a standard server load.

I/O performance for virtual machines is where InovaWave is focused. DXtreme is a shim that sits in the Windows I/O subsystem, speeding up I/O requests with intelligent caching and predictive block retrieval. Essentially, DXtreme gives a standard I/O device some logic specific to virtualization loads.

Today DXtreme is limited to 32-bit Windows hosts and virtualization platforms that run on Windows. But although the initial market is small and the product very new, hopefully the coming months and years will bring InovaWave's innovations into the broader market of VMware ESX, Xen, and other Linux-based VM solutions, because if my testing is any indication the company has made significant strides in improving I/O subsystem performance for virtualization workloads.

Virtual servers, real results

I prepared my test bed by building an HP ProLiant DL585 with Windows Server 2003, and installing VMware Server 1.0.2. The ProLiant had four dual-core Opteron 885 CPUs, 16GB of RAM, and the HP SmartArray 5i SCSI RAID controller, driving four local 36GB 15K RPM U320 SCSI drives, and a link to an iSCSI target running on a Network Appliance StoreVault S500. I used VMware due to its prevalence, although InovaWave also promises compatibility with Microsoft Virtual Server and other Windows-based hypervisors.

The VMs under test were running Windows Server 2003 and Fedora Core 5. The fact that InovaWave only supports 32-bit Windows hosts and guests is somewhat troubling, as production virtualization deployments are increasingly likely to be built on 64-bit OSes, and the numbers favor Linux rather than Windows as the host platform of choice. InovaWave’s path to supporting 64-bit host OSes is clear, and they claim to be moving a 64-bit version into the beta stage in May. Linux and Xen support are also on the road map, but functional code isn’t likely this year, which isn’t surprising, because support for Linux means rebuilding DXtreme from scratch. Last but not least, InovaWave says a beta that will support VMware ESX Server 3.0.1 is right around the corner.