OpenVZ Project Gets Migration Feature, Supports Fedora Core 5

Published: April 4, 2006

by Timothy Prickett Morgan

The OpenVZ virtualization project yesterday announced that one of the key goodies that has been shipping in the commercialized Virtuozzo virtualization tool for Linux and Windows will be made available to the open source OpenVZ community. That feature, called zero downtime migration, allows a running virtualized environment on one server to be transported on the fly to another server equipped with OpenVZ partitions.

The OpenVZ project was sponsored by SWsoft to help spur the adoption of its variant on the virtualization idea for servers. While the VMware and the open source Xen hypervisors create virtual machine partitions that run whole stacks of operating systems and their file systems and applications inside a partition, the Virtuozzo product that was created by SWsoft a number of years ago puts virtual machines atop a common kernel and file system. Each virtual machine thinks it is the whole machine, but it is just a trick of software. This is very much like the approach that Sun Microsystems took to create its Solaris containers in its Solaris 10 Unix variant and is similar to the "jails" that are used in the open source BSD Unix environment. SWsoft calls these containers "Virtual Private Servers" when running on its Virtuozzo virtualization software, which is available for Linux and Windows. In December 2005, SWsoft took the core hypervisor piece of its Virtuozzo product open source and created a project site for it called OpenVZ. The commercial Virtuozzo product includes the automation and management features that make OpenVZ a commercial-grade product that is worth some money. Virtuozzo also runs on Linux and Windows, while OpenVZ only runs on Linux.

Both SLES 10, due in May or so, and Red Hat Enterprise Linux 5, due at the end of the year, are expected to use something very close to the official Linux 2.6.16 kernel, but how close they get depends on a lot of factors--including how other virtualization features such as the Xen hypervisor are woven into the fabric of these two dominant Linux distributions.

Of course, the people behind the OpenVZ project think that for many customers, the VMware and Xen approaches, where the entire stack is virtualized and run on a separate kernel, is overkill. To be sure, admits Kolyshkin, some customers want to run Solaris, Windows, Linux, and NetWare on the same machine for development, but in production, he says companies tend to pick one operating system platform per machine and then they want to virtualize that to drive up utilization. "In many cases, it just doesn't make sense to run multiple operating system kernels."

While SWsoft, like other open source companies that offer commercial products, is keeping some of its technical goodies to itself so it can have a product to sell as well as getting support fees for the commercialized product, the company is nonetheless being generous with a key feature: zero downtime migration. While VMware has a similar feature for its ESX Server hypervisor and management tools (which are called VirtualCenter), the equivalent feature, which is called VMotion, costs money. A VMware ESX Server stack for a single two-socket server can cost as much as $4,000, and there is no open source version of VMware's code to play with. VMware has offered a rebranded version of its GSX Server, now called simply VMware Server, for free. But this product does not deploy on bare metal and requires customers to run virtual machines inside a host operating system environment, which introduces a single point of failure to the virtualized environment. (Then again, so does having a single operating system kernel and file system, as Virtuozzo, OpenVZ, and Solaris containers do.) In any event, SWsoft is contributing the code for this migration feature into the OpenVZ project, which was introduced in Virtuozzo only in February.

"We want to show people that we have unique technology and that we are very committed to open source," explains Kolyshkin, who adds that the commercialized Virtuozzo tool has advantages of its own that make it worth money, such as a sophisticated graphical interface, support for Windows, and richer support options, to name three. What makes the OpenVZ and Virtuozzo zero downtime migration feature interesting is that it does not require any particular hardware to work; it can work over whatever network connection you provide between two machines. He says that with VMware's ESX Server, you have to have dedicated shared storage between the two machines that support the mobile virtual environment, and you often need multiple network connections. "We do not require anything special in the hardware for live migration," says Kolyshkin.

Kolyshkin says that another advantage that OpenVZ and Virtuozzo have over Xeon and VMware virtual machine partitions is that you can run hundreds of domains on a single physical box. He claims that you can put up to 150 virtual partitions on a server with 1 GB of main memory using OpenVZ, and says that the overhead of Xen and VMware hypervisors prevents them from cutting up a server processor into such fine grains. The ability to dice and slice a server in such a fine-grained manner is why Virtuozzo has been popular among service providers. Of course, with the coming support of Intel's VT and AMD's AVT hardware-assisted instruction set virtualization, which will be available in volume server processors that roll out starting in the middle of this year, VMware and Xen hypervisors will get a lot more efficient because they will not have to implement so much virtualization in software; they will just access chip features that do it for them. Kolyshkin was cagey about exactly how VT and AVT will affect OpenVZ and the commercialized Virtuozzo product, if at all. "We will definitely be using it," he says. "And we will be using it to improve performance in some situations."