The following is quoted from a FAQ on a VPS provider's site:

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Q. How fast are your VPSs?

A. Our VPSs are the fastest in the industry. We run the Virtuozzo Linux kernel, which provides VPS services within kernel mode, the same way VPS services are offered on mainframe operating systems that pioneered this technology.

Anyone claiming to offer VPS services using, for example, UserMode Linux (UML) or VMWare, are not offering a true VPS. These systems run the VPS in user-mode, which takes a significant performance hit since every system call goes through a user-mode abstraction layer -- that sucks!

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(end quote)

I would be interested in a technical evaluation of this answer from someone from linode and/or anyone competent to do so.

I am more interested in an evaluation of each from a performance standpoint rather than getting hung up on what deserves to be called a "true VPS" or not.

Thanks,

Mark

Yes, User Mode Linux virtual servers run in user mode and yes, this means that system calls go through an abstraction layer. UML performance hit is nothing like the performance hit of running something in VMWare. Even though there is a performance hit for running the virtual server in user-mode you have too look at the technical merits of such a solution. This helps balance resources giving each virtual server a shot at system resources.

Another point as it applies directly to Linode is the number of users on a single host. Christ doesn't over sell a particular host server as is very common in the hosting industry. In fact when he was working through some performace problems he even under-sold the hosts to ensure a higl level of service. I believe there is still an offer for a full refund in 7 days or some such if you aren't satisfied. You should check it out, you might be suprised

Even if I wasn't in the UML business, I would say that out of any of the virtualization technologies, UML more truely represents a dedicated server than the others...

Here's a post you might be interested in:
http://www.linode.com/forums/viewtopic.php?t=351

UML does have a performance hit. There are other advantages to UML, so it depends on what you're after.

-Chris

Thanks for your replies.

I am not sure how a 'system call' would be defined in this context. Does accessing the file system involve system calls for this purpose?

Specifically does something like opening a connection to a MySQL database and reading records from it occur on top of the abstraction layer or rather is it the kind of thing that suffers performance wise under UML?

System calls are made when accessing resources that the kernel is responsible for. So yes, accessing the filesystem, or creating a network socket would generate calls into the kernel.

If you strace a process it will show you the system calls it makes ... for example "strace ls /" would show you the system calls involved in executing "ls" against the root directory...

OTOH, all the logic and code inbetween each system call runs at full steam.

Virtuozzo is pretty expensive -- that means either the extra costs are transferred to the end-customers, or the servers are loaded up to compensate. One could argue there is less overhead with Virtuozzo therefore they can fit more users onto a machine, but that increases the number of customers potentially sucking up resources away from you.

If one's only requirement is performance, they should be looking at dedis anyhow...

-Chris

I am assuming that's a typo - unless you're trying to flatter Chris in the biggest way possible

I'm not seeing a typo there.

I had a site hosted with a standard web hosting provider and a quick look on the filesystem revealed over 300 users, netcraft reported 280-something sites being hosted on the ip so it is a fair bet that over 300 sites were being hosted on it. Regardless of the hardware disk i/o is going oto be a serious issue on something hosting that many different sites.

I think he meant the typo was "Christ", not the overselling of servers...

_________________
Programs that crash have been proven to be less useful than those that don't.
• Apple TechNote 117 •

pwahahaha... I didn't see that one. That is terribly funny, now just to decide if it is merited. I'm 40/60 heh.

Thanks wazdog for helping me out there

I am a customer of a company which has the text which you quoted in its FAQ.
So I asume we are talking about the same company.

I also had to think alot if I choose Linode or that one.

Virtuozzo in fact has a great performence. I dont think that UML can beat that even when they try to compensate with fewer customers per server.

The big disadventage with the Virtuozzo host is that you are stuck with an old 7.1 RedHeat dispro (you can not switch to any other dispro like you can at Linode).