While on the hunt for an entry VPS solution for one of the external projects, I came across a very interesting observation that was shared with me today: VPS is apparently being oversold.

That struck me as surprising. While I can understand how and why some would oversell shared reseller packages, but how can a company oversell VPS? In other words, if there is a total of 1000 GB bandwidth on a dedicated box, having even 5 VPS customers with 250 GB limitation on that box (just 1 client more) - that can come up to a quite an error margin... 25%.

Isn't that a little more edgy to take a risk with?

Well, I'm not sure if all VPS technologies permit overselling. However, on the ones that do, be sure that some hosts will use it.

If only 25% overselling would be a standard... I'm sure many go way beyond that.

It's not a lot different than shared overselling.
I would be very surprised if there were VPS providers that don't oversell.

If you look at the price that VPS providers are charging these days and compare it with the price of a Virtuosso license you will see that most wouldn't be profitable with some overselling.

I have VPS with a few different providers. I assume they are overselling but as long as my service is OK I have no problem with it.

Well, as with anything in hosting or in life, what are the chances of a customer using 100% of what he's given? Assuming that on average the customers use 90% of what they're allocated (huge number), the host would still be able to safely "re"sell the remaining 10%. That could be 10% of pure profit, and from a business point of view, it doesn't make much sense not to take advantage of the situation (except if the marketing is focused around a "no overselling" policy).

This is of course an oversimplification, but the principle does apply.

Hosts that use Virtuozzo usually oversell on RAM. They even advertise "Burst RAM". If you want a true VPS, go for a Xen based VPS. Xen based hosts can't oversell on RAM.

That's very true!

I mean, how many people use unlimited MYSQL, Emails, Subdomains. I'll be lucky if I even use more than 10 of each. As for bandwidth and space, most of us have an approx estimate of what we might need. Usually we set a higher limit, just incase we need more. The truth is on average, hardly any users will be lucky enough to use more than 75% of their resources. Mabye in the long term you might, but "usually" starting off, you just don't pull that kind of traffic.

Why is that? What is special about Xen?

It is just the way that the virtualization software was coded in Xen. A Xen VPS normally costs a lot more money than a virtuozzo or OpenVZ based host.

Xen's virtualization model has a swap file for each vps and allocates basically the ram the vps is configured for. This has plus and minuses as you can't easily burst.

Since most computing is bursty, meaning it isn't a flat line for cpu or ram usage openvz is popular for the host given the ability to oversell a bit.

It is more popular for the customer (if they chose a good host) in that you can have lets say 1/4 of a cpu guaranteed and 256mb ram but burst up to the capacity of the machine. This means on a vps server with 4 cpus and 16gb ram if you have it setup like this, you could use the full 16gb (assuming no other processes are using it) for a brief moment which would allow processes to complete faster.

Virtuozzo can be easliy oversold. In fact in there business model they present to you when you buy the software from SWSoft states that you should have 30 VE licenses on all of your boxes. I was told that if I did not have 30 VE licenses on every box I was loosing money. More like they are loosing money.

They base this off of a Dual Xeon 2.8GHz with 6GB of RAM.

Let me tell you on our nodes there is no way we could ever put that many on one node without causing issues for clients or overselling. I guess you could if they were all 128Mb and 64MB VPS servers but who actually buys or uses those. We removed our 128MB VPS plans becuase they were hardly ever purchased and most of the control panels want at least 256MB except for Direct Admin or Wedmin.

We put no more than 20 on a node and we have never even done that. The only way you could get 20 with normal use VPS servers meaning 256MB and 384MB and a few 512MB servers is to run something like Dual Xeon Woodcrest 5150 or 5160 CPU's with 8GB or RAM and 4 500GB drives in a RAID 10. I guess maybe the top of the line quad core Clover Towns with 8GB of RAM might be able to push 30 VE's if they were not all really busy and not to many of them were 512MB servers. To not oversell I would stick to 20 a node.

In most cases the choke point of a hardware node will be in disk read and write and with CPU usuage. Memory is usally not the choke point.

So yes VPS hardware nodes can be overslold and SWSoft pushes that model. In fact there licensing pushes that model since you can only buy 1, 3, 5, 10, 20, 30, 50 VE licenses I believe. I would say that the 20VE license is the most popular.

Does OpenVZ come with some type of a GUI panel?

No, OpenVZ doesn't come with a Power Panel like Virtuozzo does. However, there's a third party one out there called HyperVM. It's pretty good in my opinion and you can find it at http://lxlabs.com

OpenVZ and Hyper VM do allow overselling. I know because I use the software. That said I do not oversell. Also as was stated in the above posts Xen has disadvantages over software that does not oversell. I can allow a customers RAM to "burst", meaning if another client is not using their RAM at the moment you can borrow some of it. When they need the RAM allocated to them, they take it back because you both have priority for the guaranteed amount of RAM.

Hi,

Xen is better than virtuzzo..virtuzzo allow over selling..

Regards
Jeff

I'm not so sure about that. Lately, I've seen a slew of hosts that use Xen virtualization that are much cheaper than Virtuozzo, and at least on the same level as OpenVZ. It's been known for a while that Xen isn't the fastest VM (it still is pretty speedy though), but I think it's coded with more 'isolation' in mind.

But even if you find a great price on a non-Xen VPS, you have to remember, you may not get your full RAM.