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"Are OpenVZ VPS generally oversold?", this is the title of the thread opened by Web Hosting Talk's member "Continuation". "With OpenVZ there's really no "guarantee" of the amount of RAM you're getting, correct?", asks the forum member. He says that he wonders if overselling is common for OpenVZ VPS Hosting plans. "If a VPS node has 8GB of RAM, how much OpenVZ "guaranteed RAM" will be sold on it? Is it common to sell, say 12 1G RAM VPS plans on a node with 8GB RAM?" is the question asked by "Continuation".
He also asks how can he find out if there's any overselling going on in an OpenVZ powered VPS? "What's your experience?" is the question to the community.
The user's PS note is: "On a related note, if there's no real "guarantee" with OpenVZ, then what's the point of buying a 1G RAM plan instead of a 512M plan? Would I really be getting more RAM? If so, how does that work?""
"OpenVZ does have beancounters available for hosting providers to restrict the amount of RAM to your container - Thus, you do have a "guaranteed" amount of RAM which you can access and this is all your container sees. This means that a 512MB VPS will definitely not have access to the same amount of resources as a 1GB VPS", explains SC-Daniel from ServerComplete.com, a provider of Windows virtual private servers.
He adds that OpenVZ does allow for overselling and does not completely "guarantee" the allocated RAM on the node, like Xen. "It is unfortunate that a lot of OpenVZ providers do oversell/oversubscribe their hardware which leads to major performance issues" says SC-Daniel.
According to the WHT member "All boils down to ethics", and If a web hosting provider claims they do not oversell then the customer will need to take their word for it.
UNIXy, a forum member from Houston, Texas with status "web hosting master" comments that the conclusion "With OpenVZ there's really no "guarantee" of the amount of RAM you're getting, correct?" is incorrect. "You can guarantee resources with OpenVZ the same way you do with Xen. Extra steps are required to achieve the result. We do this at VPS Lux and it's working well. Actually, we disable burst altogether" says UNIXy.
He adds that anyone can sell 12 GB burst RAM on an 8GB box, but it will be a problem "waiting to happen". To the question "As a customer how can I find out if there's any overselling going on? What's your experience?", the Unixy.net's representative answers "/proc/user_beancounters is your best friend in this case since it doesn't lie. It's a kernel interface that server administrators can't just reset without rebooting the VPS. Always keep an eye on the failure count (failcnt). Here's a reading: http://maxgarrick.com/understanding-...source-limits/".
UNIXy also replies to the question "If there's no real "guarantee" with OpenVZ, then what's the point of buying a 1G RAM plan instead of a 512M plan?". He says that there's a guarantee. If anyone buys a 512MB / 1GB non-guaranteed RAM VPS hosting plan (overseller will advertise is as 1GB RAM), the customer is guaranteed 512MB of RAM. "Anything above 512MB is on best-effort basis. So, if the server is oversold and everyone else is maxing their allocated guaranteed memory and more, you'll never get a chance to burst above 512MB", ads UNIXy. /proc/user_beancounters fail counter will increase and VPS stability becomes an issue.
The next comment is from Host Color (a company, advertiser in VPSHostingDir). Its representative says that OpenVZ is just a technology, and the managers of web hosting companies are those who oversell because they do not want to invest in reliability and in quality service. "OS virtualization is an excellent virtualization approach that offers more scalability and the opportunity for web hosts and VPS owners to dynamically increase resources", comments the WHT member and ads that OpenVZ and OS virtualization does not stimulate overselling.
Another WHT member with the nickname Fizzadar says that "Most providers oversell a little, it's server-efficient, there's nothing wrong with that".
The next one is "Continuation", the one who opened the thread. He says that he understands that the "burst" RAM is not guaranteed and explains that what he is trying to understand is that if the "guaranteed" RAM is really guaranteed.
"For example, is it possible for someone to sell 12 "512MB guaranteed, 1GB burstable" plans on a 4GB RAM node? If it is, then the "guaranteed 512MB" isn't really guaranteed, because 12*512 is 6GB, larger than the amount of physical RAM on that node", is the next question of "Continuation".
"Sorry I misunderstood your question. Yes, it is possible. As far as we're concerned, we're preventing this situation by limiting the number of VPS per server to 8.", is the response of UNIXy,
Before his reponse TonyB from HawkHost writes "That is exactly what is done in a lot of cases. Each user has 512MB but most are using 200MB so the provider gets away with it. It becomes even easier when you're dealing with machines with double digit GB amounts in memory". He explains that most slow VPS's are caused by I/O issues so the drives are to slow. "You can get a server with 24GB memory and just a single 1TB machine and it'll get slow from the drive not being fast enough", says TonyB.
RavC asks UNIXy "Why not just use Xen if you are going to all this trouble of disabling burst RAM, restricting users of your node, and not overselling"?
"Here are some reasons", responds UNIXy and says that OpenVZ causes lower overhead because of the "container" approach; explains that OpenVZ features with better raw performance especially when there is no overselling; points out that OpenVZ has quasi-native IO performance and has better management tools (vzdump and vz*), and finally that OpenVZ is easier to setup and has better native backup tools.
"All of this helps us focus efforts on pleasing customers. With that said, we also have Xen servers for customers that request it", adds UNIXy.
Unfortunately Web Host Use OpenVZ to Oversell?
Rick-RikeMedia comments "Unfortunately due to the nature of OpenVZ, a lot of providers do oversell. Some oversell to the point that VPS accounts become almost unusable. You'll find a lot will also offer large amounts of RAM, but very low CPU allocations, in the hope that you'll be a very light user".
He adds that very few hosting providers are going to admit they oversell, and some will just lie outright and say they don't. "The only way to really tell, is to read the reviews, and try out the service", says The WHT member.
Another forum member with nick name "aeharding" posts that he could almost guarantee if it's OpenVZ, then it's oversold. "The actual variable you're looking at is how responsible they are at overselling" says "aeharding" and posts "For example, FSCKVPS oversells, but their servers are very, very fast even though they are. There is no problem with overselling. It makes a server actually utilized. However, it does matter the amount of overselling".
"I'm sorry but thats completely wrong. We use OpenVZ, does that mean we must be overselling? No", is The response of Rick-RikeMedia. He says that anyone can not "almost guarantee" as you they don't have first-hand experience with the operations of any other VPS hosting provider.
"I know many providers, who like ourselves will refuse to oversell on principle. Even budget, or unmanaged VPS providers don't have to oversell to turn a profit you know. I'll admit that there are a lot of vps hosts that do oversell....but a lot of shared and reseller hosts also oversell, its just the way it is", comments Rick-RikeMedia, who's representative of VPSSpreed.
Overselling allows clients to pay less for resources?
A forum member with the name "WaferVPS" who represents a company with the same name expresses an interesting, but controversial point of view. "The blind prejudice towards the concept of overselling some people show astounds me immensely! Overselling when done properly benefits the client a lot, and there are plenty in the business who do it properly, enough at least to make this unrelenting stigma irrelevant", posts "WaferVPS".
He adds that overselling allows clients to pay less for resources that they use less often, and ads "I don't understand the difficulty of the concept".
"Agreed. With huge, powerful servers, over subscription (that word has a slightly less negative connotation) is a must. Over subscription of any amount on a wimpy server is sheer folly" says "advantagecom" while posting a comment to WaferVPS's post.
"When you look at populations, the larger populations become more statistically predictable as a group. The converse is true with smaller populations. That's why over subscription can work on a big node, but causes problems on a small node", explains "advantagecom".
He says that if anyone has a "monster server with 8 processors, 32GB of RAM, and a 20 disk 15K RPM SAS RAID10 backing it", they can have a larger population of VPS on the node. If you track your usage on the node properly, you can leave enough capacity to absorb the usual spikes.
"The common argument against over subcription is "What if everyone used everything they purchased all at the same time?" That's a farce. It's not going to happen unless it is just a single client using all those VPS as a cluster. Who has *that* on their server? That said, Xen is generally less oversubscribed simply because the ability to oversubscribe RAM in Xen is not yet fully developed. That's the primary reason you see Xen VPS that are roughly 6 to 10 times more expensive than an "equivalent" OpenVZ/Virtuozzo VPS. You can expect pricing of Xen VPS to come down as soon as that feature works right", explains "advantagecom", who's real name is Andrew.
User "VPSVille" responds to "advantagecom" that "OpenVZ providers do not need to oversell to turn a profit, but some do". He adds that it is not about overselling, but about misconfiguration, which causes instability and poor performance.
"It doesn't have to be oversold to be slow, and the technology doesn't really matter as much as the people behind the service", adds "VPSVille".
The WHT member named "Mugo" provides "Short answer". "If the entity has been around for a while, and no one is complaining about performance, they either don't oversell or know how to do it effectively", he says.
"Mugo" adds that just because "OpenVZ is used doesn't mean it's oversold". "I've planned, and used, many facilities that put a very set number of VE's on a node. They put 2-5 on a high powered node, get a good profit per server going, and have happy customers that stay", writes Mugo.
He comments that if a web hosting provider grossly oversells, it generally don't last long. "Clients either get fed up, or equipment breaks (should be noted most blatant over sellers usually have no backup strategy) and they never recover, folks scatter away, and other companies absorb or outright buy the flailing company", explains "Mugo".
He gives and example for an abusively overselling company's inevitable thread life cycle: "Node / Network down > Cries for help > Insufficient DR discovery > Cries of dissatisfaction > Wait w/ no resolution > Insults thrown back and fourth > Clients scatter to the winds or endure company merge".
"Many can sadly testify to the ever-repeating chain, especially with the kiddie hosts", finishes "Mugo" his post.
OpenVZ is an OS-level virtualization technology based on the Linux kernel and operating system. It can be described also as "container-based virtualization for Linux". OpenVZ creates multiple secure and isolated OS instances (containers, Virtual Private Servers (VPSs), or Virtual Environments (VEs)) on a physical server.
Compared to other virtualization technologies such as VMWare's approach and paravirtualization method used by Xen, OpenVZ is "limited" as fas as it requires the physical server (host) and the Virtual Private Servers (guest) to run Linux OS. Different Linux distributions can be used on the server and on each container.
OpenVZ - A Better Performance?
However, OpenVZ has one main advantage. It claims to produce better performance. The OpenVZ website says that "there is only a 1% to 3% performance penalty for OpenVZ as compared to using a standalone server. Test conducted from independent 3-rd party entities show that this evaluation is correct although some say that there are "more significant performance penalties".
OpenVZ's concept is in the core of one of today's world's leading commercial OS virtualization solutions (and one of the most popular Virtual Servers platform as a whole) - Virtuozzo Containers, a branded software product by Parallels.
It is Open Source!
The good news for web hosting entrepreneurs and software engineers interested in virtualization technologies is that OpenVZ is licensed under the GPL version 2, which means its basis can be used for the development of another virtualization software.
The OpenVZ's virtualization method to use Linux kernel and Linux OS enables better utilization of the hardware resources and avoids conflicts between software applications. Each container (VPS) runs as a stand-alone server. Containers (Virtual Private Servers) can be rebooted independently and their owners have root access, create users, have own IP addresses, memory, manage processes, files, applications, system libraries and configuration files.