This is a really interesting article, as the gloves come off and the bell rings - SWsoft's CEO comes out swinging... describing what he believes are the advantages of using Virtuozzo over VMware.  One of the issues that Virtuozzo has the advantage - ease of management and cost.  Because of the way Virtuozzo virtualizes, patching an operating system becomes much easier, because you only have to patch the "host", rather than both the host server and each virtual machine residing on that host.  And because they claim to be less resource hungry than VMware's product, you should be able to fit more virtual machines on a physical box, and you shouldn't need as big or beefy a box (translation, less $$$).  VMware throws a punch back, but I don't see this fight ending in one round.  Check out the article, it's a good read.

Quoting from TechWorld

VMware's virtualisation software, which leads the market by a considerable margin and is fast becoming the platform for server consolidation projects, is too resource hungry, too slow and too expensive, according to the boss of a much smaller virtualisation company.

Serguei Beloussov, CEO of SWsoft which sells virtualisation product Virtuozzo, has slammed the virtualisation industry's standard-bearer, saying that Virtuozzo's OS shim-style virtualisation is better than VMware's all round, in that customers can fit more virtual machines (VMs) into a server, and that it's easier to manage and so costs less to run.

Beloussov, who claimed that analysts report Virtuozzo as second on enterprise's product short-lists behind VMware, said that VMware's primary product, ESX Server, is too expensive in terms both of total cost of ownership and of hardware. This is because of the way that ESX Server works, reckoned Beloussov.

Each VM contains its own version of the OS, which takes management and needs patching and periodic updating, according to Beloussov. When you multiply that up by the dozens of VMs, the management costs multiply. "If you have 1,000 servers each with 20 VMs, it means you have 20,000 OSes to manage", he said. "With Virtuozzo, you have just 1,000 OSes to manage."

Beloussov also said that he had spoken to customers who wanted to fit ten virtual machines into a single server and found that the hardware costs of doing so became prohibitive. "It can cost from $40,000-$50,000 per server plus storage and network once you add in the extra memory and processors," he said.

He then claimed - as you'd expect - that Virtuozzo was better because it suffered from none of these drawbacks. "We find customers set off to solve the problem of physical server sprawl. They then get OS sprawl - we solve that," he said. This is because, according to Beloussov, Virtuozzo consist of a shim between the OS and the VMs that allows one OS kernel to be shared across VMs. With only one kernel running, hardware and maintenance costs are lower, if Beloussov is to be believed.

There's little hard data to back this up other than a degree of common sense -- if you only need one OS kernel it will be less resource-hungry, so it figures that you could pack more in, and that it would take less management time.

Additionally, you get a choice of OS with VMware but, with Virtuozzo, each VM runs on the same underlying OS kernel. Beloussov reckoned this was not a problem for most businesses who were likely to run the same OS on a virtualisation platform anyway.

"Customers don't mind having all their Windows systems in one place and it's same with Linux. I'm not sure you'd want to mix the two in production environments", he said. "The only problems we do see are in test and development environments where performance and security aren't a problem - we're not as good as VMware there."

On the other hand, VMware reckons its approach is more robust. With Virtuozzo, if the OS kernel falls over, all the VMs are wiped out. This not possible with VMware's ESX Server because each OS is self-contained and runs above a VMware hypervisor.

Finally, Beloussov's comprehensive demolition job on his biggest competitor cited performance as another weakness. "VMware is I/O intensive", he said, claiming that its overhead could be 5-10x higher then that of his own product. "The problem is that you cannot find out because the VMware licence agreement means you can't publish performance comparisons," he said.

The original source article can be found, here.