VPS Virtualization Technologies
As mentioned on the previous page, Virtual Private Servers employ a technology known as virtualization, which is the process where a physical server is divided into virtual divisions (sometimes called "containers"), making it appear as if your site is running on a dedicated server.
If you're familiar with the concept of how a large hard disk drive is partitioned into smaller logical drives, you have an idea how virtualization works.
Let's take a closer look at the main players in the virtualization game:
Virtuozzo
• Virtuozzo (by Parallels). This is the software WiredTree uses. It's what most VPS hosts use. Virtuozzo is not free. Efficient use of server resources is it's primary strength (far as you & I are concerned).
On the downside, it makes it easy for a greedy web host to "over-sell" a server, thereby diminishing any performance advantages it might otherwise hold. Since hosting companies are in business to make money, the temptation to squeeze out every last dime from a given server must be great.
This is why hypervisors are becoming popular. It is more difficult to over-sell a hypervisor. If your hosting plan offers burstable memory, it is NOT a hypervisor, cuz hypervisor-based accounts come with fixed memory limits.
Burstable limits allow other accounts on your physical server to borrow your "unused" memory .. on an as-needed basis. Many consumers do not like the idea of another account using memory they pay for .. even if they're not currently using it.
They worry a web host (who is obviously in business to make money) may secretly tweak their RAM-allocation settings (which they *do* have control over) to artificially lower their memory usage .. thereby allowing them to allocate part of their RAM (that they're paying for) to other account$.
OpenVZ
• OpenVZ (also by Parallels). This is the open source version of Virtuozzo. It comes sans (without) the high-end features that accompany it's expensive big brother.
Xen
• Xen (open source). Cool name. A hypervisor. Primary strength is that it's hard to over-sell a hypervisor. You can be fairly confident you're getting what you paid for. Since Xen is open source software, the concept of maximizing profit$ do not play a dominant role in its development.
On the downside, this stricter compartmentalization leads to less efficient use of server resources when compared to Virtuozzo.
Many side-by-side comparisons have been performed and debated in hosting forums online. Server configuration obviously plays a big role in these comparisons, and you obviously have to look at WHO is doing the comparison, and whether they configured each server for optimal performance. A slight tweak can kill performance.
I have heard many claim their site's responsiveness improved dramatically after moving to a Xen-based server. I would like to try one .. just to see for myself if I can notice a difference.
In the larger scheme of things, I think most feel that a Virtuozzo-based VPS that is NOT over-sold will perform better than a Xen-based VPS .. but that Virtuozzo-based servers make it hard for web host to resist over-$elling .. thereby diminishing any performance advantages they'd otherwise see.
VMWare
• VMWare. Generally considered the most mature virtualization software on the market. Also the most expensive. Probably the closest you can get to a true dedicated server in a VPS environment. Like Xen, VMWare is also a hypervisor.
VMWare offers many different versions of its virtualization technology. At least one of these appears to be free.
With VMWare you *can* change your version of Linux, as with Xen also, I believe (tho not positive), tho your host may only support one particular distro/version. [WiredTree uses CentOS 5.]
Some people say VMWare is the only software that can truly be used in conjunction with the term "virtualization".
Disclaimer
Let me conclude this page by saying I have no first-hand experience with any of these products except Virtuozzo. Normally I'm reluctant to discuss things for which I have no first-hand experience. But I spent considerable time researching the topic (because it interests me).
If you find inaccuracies here, please report them. Most of the guides here have been greatly enhanced by reader feedback and input.
On the next page, we'll look at "burstable memory" and discuss disk I/O bottlenecks, which are typically the biggest hindrances to performance in a Virtual Private Server.