VPS Guide






Guide to Virtual Private Servers: VPS Web Hosting Providers: Page 12

VPS Guide






Guide to Virtual Private Servers: VPS Web Hosting Providers: Page 12

Virtualization Technologies for VPS Web Servers

As mentioned on the previous page, Virtual Private Servers employ a technology known as virtualization: a technique whereby a physical server is divided into virtual divisions (sometimes called "containers" or "virtual environments"), which make 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, along with their respective strengths & weaknesses:


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 its primary strength.

On the downside, Virtuozzo makes it easy for greedy webhosts to "over-sell" a server, thereby diminishing any performance advantages it might otherwise offer. Since hosting companies are in business to make a profit, the temptation to squeeze every last dime from a given server must be great.

This is why hypervisors are becoming increasingly popular. It's more difficult to over-sell a hypervisor. If your hosting plan offers burstable memory, it is NOT a hypervisor, because 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 paid for .. (even if they're not currently using it).

They worry a greedy webhost (who is obviously in business to make a profit) might 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$.

If you signed up for a hosting plan that comes with 512-MB RAM, but your actual usage never exceeds 256-MB, it that because your site/account doesn't really need more than 256-MB? .. Or because your host has tweaked your memory allocation settings to artifically lower your RAM usage? (and has assigned 256-MB of the memory that you paid for to another account.)

Reading threads at various online forums around the web, you get the idea that most webmasters feel ALL webhosts are over-selling, which leads to a search for the "one true host" (who doesn't over-sell their servers).


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.

It would stand to reason then, that webhosts who use OpenVZ should be able to offer comparable plans (memory, disk space, bandwidth, etc.) at a discount to those hosted by Virtuozzo.


Xen (open source). Cool name. A hypervisor. Primary strength is that it's hard to over-sell a hypervisor. With Xen (and all hypervisors) you can be fairly confident you're getting what you paid for. Xen is open source software, so the concept of maximizing profit$ do not play a significant role in its development.

On the downside, this stricter compartmentalization leads to less efficient use of server resources (compared to Virtuozzo and OpenVZ).

Many side-by-side comparisons have been performed and debated in online hosting forums. Obviously server configuration plays a big role in these comparisons, and you have to look at WHO is doing the comparison (bias?), and determine whether each server was configured for optimal performance. A small tweak of configuration settings can kill (or boost) performance results.

I have read many threads and heard many users claim that their site's responsiveness improved dramatically after moving to a Xen-based server. Naturally I would like to try a Xen-based server .. to see (for myself) if they really offer such a noticeable performance difference .. because a responsive server makes a monster difference in user enjoyment. And nobody likes a laggy site.

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.

Of all the virtualization products listed on this page, Xen is the one I know least about.


VMWare. Generally considered the most mature virtualization product on the market today. Also the most expensive. VMware is the closest you can get to a true dedicated server in a VPS environment. Like Xen, VMWare is also a hypervisor, and all the pro's and con's of hypervisors mentioned for Xen also apply to VMware.

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VMWare offers many different versions of its virtualization technology. At least one of these appears to be free.

With VMWare (and Xen) you can change your version/distro of Linux, tho your host may only support one particular distro/version. [WiredTree uses CentOS 5.]

As a point of contrast, with both Virtuozzo and OpenVZ you can only use the version/distro of the operating system (Linux, Windows, etc.) that is used on your server, because all sites/accounts on the server use the same operating system.

If you wanted to use a different version/distro (operating system), your webhost would have to support that option, and they would have to move your site/account to a different (physical) server.

Some people say VMWare is the only software that can truly be used in conjunction with the term "virtualization".


Let me conclude this page by saying I have no firsthand experience with any of these products, except Virtuozzo. Normally I'm reluctant to discuss things for which I have no firsthand experience. But I spent considerable time researching the topic (because it interests me).

If you find inaccuracies here, please report them. (All guides posted here have been greatly enhanced by reader feedback and critiques.)

On the next page, we'll look at "burstable" memory, and what means about the performance of our Virtual Private Server.

NEXT » Allocation of burstable RAM / Memory on Virtual Private Servers

For more along these lines, here's a Google search preconfigured for the query » compare virtual private server vps vs dedicated web hosting

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