According to the demonstration, this shared-everything concept serves to significantly reduce the virtualization overhead typically seen in VMware's and Microsoft's virtualization solutions. The hypervisor concept in those two products proxies calls to physical resources from virtual machines. In Virtuozzo it isn't necessarily there, which means that any Virtuozzo virtual machine enjoys direct access to physical resources.

Because of this reduction in overhead, it is not unreasonable for a 4-way server with 16G of RAM to handle 100 simultaneous systems under low-to-moderate load. That's a far cry from VMware's or Virtual Server's count.

The biggest complaint in VMware and MS Virtual Server environments is the horizontal scaling of physical resources like chassis, RAM, and processors to support concurrent virtual machines. Virtuozzo gets around this by removing the hypervisor overhead and sharing most of the file system.

They call it their "copy on write" file system that in my impression does to virtual machines the same thing that Softricity does with virtual applications. The virtual machine can see the files and registry keys on the host system, but when it has to update one of those files it does the update to a virtual machine-specific pointer. Because only the pointers are what ends up adding to disk space, this has the effect of eliminating a lot of duplication.

Where Virtuozzo falls short in the enterprise market compared with VMware (though not Microsoft) is the ability to hot migrate machines from chassis to chassis. They can do this for Linux-on-Linux systems but not Microsoft-on-Microsoft systems. But, there is a patch forthcoming that is supposed to enable this functionality. So, watch this space for more info. Once that patch and functionality is available, I suspect we'll start seeing more of Virtuozzo in the enterprise market space.

Another limiting factor is a load distribution system similar to VMware's DRS. Though no plans for one are forthcoming, I suspect market demand will soon have them looking into this possibility.

In short, is SWSoft Virtuozzo a compelling product? Absolutely. But again, in a market where all the name recognition goes to the VMware crowd, they're getting downright squashed in adoption.

I should be getting a set of licenses soon to evaluate the product more fully in the next few weeks. Once I get them installed and checked out, I'll write again on this interesting product.

Check out their web site at: http://www.swsoft.com/

UPDATE (3/7/07, 9:37a): Forgot to mention one other really nifty feature. Unlike with other virtualization systems, Virtuozzo has the ability to dynamically change resource loads on the fly within a single system. So, if your virtual machine needs another 256M of RAM right now, you can just add it and it recognizes the additional RAM. No reboot necessary. This works with RAM count, processor, and even disk size. Pretty impressive.