Pro and Cons of Virtual Private Servers (VPS) for OpenSim

When you have a look at the OpenSim hosting market today, you quickly recognize two kinds of hosting providers. One group of providers offers OpenSim based on dedicated server hardware, while the other group of providers offer OpenSim on so called Virtual Private Servers (VPS), where many such virtual servers run on a single hardware server. The second group of providers mainly tries to sell OpenSim through low prices.

The question is, if Virtual Private Servers (VPS) can be a cheap alternative to dedicated servers for OpenSim or in which situations it might be an alternative.

Virtual Private Servers

VPS is a technology that was developed for cheap web hosting by being able to share expensive hardware resources by as many web servers are possible. Compared to basic web hosting services, it additionally allows the web site provider to use some advanced web hosting features, like server side scripts or to use of database storage. This are useful features for better looking and more feature rich web sites.

VPS bases on the assumption that web sites of smaller and medium sized institutions usually do not get traffic most of the time. During these times the processes of such web sites can be put asleep and the data is temporarily
offloaded on slow hard drives to free main memory for currently active web sites. This allows many web sites to share the same physical resources (CPU, memory, bandwidth), which keeps costs low.

VPS providers apply a so called Fair Use Principle. If one hosting customer uses too many ressources (CPU, memory or bandwidth) they take measures to ensure that the overuse of one customer does not affect the service quality of other customers. This can mean that the available bandwidth of that customer is cut back or that the processing power is reduced to ensure nobody else is affected negatively by that overuse.

Now the question is, if VPS as suitable for OpenSim or in which cases VPS might be an alternative to host OpenSim.

OpenSim processes, like processes of other real time applications like voice-over-ip or video conferencing never sleep like web server processes. Even if there is no visitor in an OpenSim region, a typical OpenSim process anyway constantly consumes between 0.5 and 3% processing power of a processor core.

This permanent use of processing power is untypical for web server applications VPS was mainly developed for. Depending on the kind of visualization software used, such processes are anyway put asleep from time to time, to avoid negative impact on other VPS instances, although these processes should be kept running. This is done to enforce the Fair Use Principly and to ensure that other VPS instances on the same hardware server get enough computing power and physical main memory.

As a consequence OpenSim users experience lag, because of regular storing and loading of data to slow hard drives and because of the overhead and delays of constantly having to start and stop processes.

These negative effects increases the more users are on one hardware server providing VPS services. And it gets even worse if there are more such processes overusing resources on the same server hardware. Such processes with permanent resource demands begin to fight for the sparse hardware resources, because the basic assumption that most (web server) processes can sleep and offload data most of the time is not true anymore.

Bandwidth can be another issue, because OpenSim creates peaks of data traffic. Depending on the virtualization technology used, this also causes issues, if the peak bandwidth is limited. That can cause crashes and instabilities during logins and teleports.

Because VPS tries to store data on hard drives as often as possible to safe main memory, the additional time needed to load data from that slow storage cause additional lag. The probability of such delays increases the more memory an OpenSim process uses. Bigger regions with many prims, scripts and visitors quickly become unusable because of the permanent swapping or paging of memory needed by these OpenSim process.

This effect also increases the probability that Mono threads block or crash completely, if OpenSim runs on top of Mono. This causes instabilities and more frequent crashes of OpenSim regions.

What a VPS Hosting Company Says

I had a long discussion with the CTO of a big VPS hosting company and he did clearly say: “VPS is not suitable for any real time application [voice, video streaming or virtual worlds].”

He said once they did host a voice conference on a VPS server for a customer, but that this was just done for a marketing show. In reality that customer was the only one on the hardware server used, to ensure high service quality. So in fact that customer did use a dedicated server for that marketing campaign, although it was said that it’s a virtual server.

Summary

VPS is not suitable for regions with much contents (prims and scripts) or if many visitors need to be supported. Beside that the service quality is substantially lower: Visitors experience more lag, less stability and more frequent region crashes.

On the other hand, if someone just needs a small region with not too many prims and scripts and if just 2 or maximum 3 visitors are enough, then VPS offers a cheap alternative for beginners. But most region owners will quickly reach the limit and will want to be able to add more contents to their region, without having to experience a quickly degrading service quality.

For professional users, like corporations, shop owners, dance club owners, etc. VPS is definitive no alternative for professional OpenSim hosting using dedicated server hardware.

Dedicated Servers

Dedicated servers are the best choice for bigger regions and regions that have to support many visitors.

The prices of OpenSim regions hosted on dedicated servers very much depend on the processing power, main memory and network bandwidth provided. Good offers for beginners start with 512 MB main memory per region, while the typical average users need up to 1 GB. High end users that use many prims, scripts and have many visitors need up to 2 GB of memory for one region.

General Advices

In any case be careful if an OpenSim hosting providers promises you very high numbers of prims, scripts and visitors, especially if no information about the underlying hardware platform is given or if you see that the amount of memory, the included network bandwidth or processor seem not to be sufficient for what they promise.

At the end it only counts what you get and not what they did promise you, despite how low their price is!

You should also carefully check what is included in the hosting service package. Do they ensure high availability with professional 7×24 service monitoring? What kind of web based or in-world management tools are provided? What about backups? Are optional features like voice, search, groups, off-line messages, money, HyperGrid and mega regions included?

Data backups are a must and should include daily backups and on demand backups to protect you from data loss. Database backups are the most important, because they store all important data, but customers should also be able to get backups of their region contents as OAR archive files.

Customers should also get web based and/or in-world tools to manage their regions (display status, restart, etc.) and in-world monitoring panels for regions.

Finally and most important check if they have good references for their hosting services and for customer service? Service quality very much depends on how professionally OpenSim is managed and run. Good references are an indication if a hosting provider does his job well.

Currently many OpenSim hosting companies out there have problems to deliver what the promise. With good references the chances are higher that you will be happy customer, using good OpenSim hosting services for a reasonable price.

Snoopy Pfeffer

CEO & Founder of Dreamland Metaverse
snoopy.pfeffer@yahoo.com
http://www.dreamlandmetaverse.com/

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7 Responses to “Pro and Cons of Virtual Private Servers (VPS) for OpenSim”


  1. 1 peter host June 5, 2010 at 8:58 pm

    It really depends, in my opinion on what technology you use, and what hardware it’s running on. This post is about VPS, and I won’t contradict the author on this point : if you’re booking cheap VPS, sure, you won’t have much bangs for the bucks as the provider has already squeezed its virtual servers as much as he could to sell them at ultra low price.

    If on the other hand you’re building a cloud on top of good dedicated hardware, in the same bay of a datacenter, it’s up to you to allow resources fairly.

    As virtualisation goes, there are techniques (such as OpenVZ) which enable running a linux virtual machine with almost no performance loss. Other techniques are more or less resource intensive, but as far as my testing goes, Xen is doing very well. Kvm not so well, and VMware i’m just begining to experiment with, and seems in-between. Amazon’s Cloud, which is build on top of a Xen architecture, performs exceptionally well. (but is not cheap)

    Virtualisation provides lots of advantages, not the least of which are snapshots. Sure, the need for backing up your SQL DBs is a no brainer, but hourly (differential) snapshots enables the provider to get a broken region up and running in less than 2 minutes time, with one click in an SOPA/xmlrpc driven Website.

    My tests with openvz containers show no performance lag. A 6×6 megaregion on a quadri-dual-core with 4 GO RAM (which CPU almost never is used more than 25%) and the same megaregion inside an openvz container, limited to 1 CPU and 2 GO RAM runs as fine, liberating 3 CPUs and 2 GO RAM for the cluster to use. When the load the virtual machine hosting the megaregion is high, CPU and RAM can be liberated on the fly for the duration of the resource peak, and (usually) for a small amount of time.

    But all in all, I agree with you : you only get what you’re given, and the virtualisation lingo added yet another layer of confusion in the commercial rifraf. Low cost VPS for hosting Opensim servers won’t ever compare to (even middle class) dedicated hardware. But a correctly managed Cluster of OpenVZ containers, scalable on the fly, has many advantages over the standard dedicated server in terms on overall cost (customer and hosting company), ease of deployment & backup.

  2. 2 Snoopy Pfeffer June 6, 2010 at 3:00 pm

    Peter, thank you for your comment! Good that you point out the important differences between cheap VPS hosting and high-end cloud computing solutions. My article is just about VPS and cloud computing definitively is a different story.

    High-end cloud computing comes close to the performance of dedicated servers, with the advantage that you can quickly start and stop the service or scale up and down the virtual server you use (number of cores, allocated main memory, etc.).

    Because of the principle that you just pay what you use, it can be an interesting alternative to host OpenSim regions, if such regions do not need to be online 7×24 or if the region has very much changing resource demands over time. An example are regions for events that can be shut down or at least run with less processor power and memory while there is no event.

    You also mention that good cloud computing is not cheap. I did a comparison of similar OpenSim hosting environments. The costs of cloud computing is about twice as high compared to dedicated servers, if that region is online 7×24. But if a region is not online all the required resources change very much over time, cloud computing can be an interesting alternative to host OpenSim regions.

    Anyway certain features like voice still run better on dedicated hardware. During tests we did, the voice quality was better using a voice service on a dedicated server.

  3. 3 Jef@Dnhost, Web Hosting November 16, 2010 at 12:06 pm

    Very nice article Snoopy, you have a good point but I also agree with Peter Host; it all depends on what hardware the Provider hosts Opensim and how packed it is with other VPS’s.

    Quality hardware, lightspeed network and well structured VPS/clustered VPS solutions will always make a difference compared to very low-price VPS offerings, in terms of performance, management and uptime, not only for clients hosting OpenSim regions but for any intensive online application.

  4. 4 Tony July 11, 2011 at 5:26 pm

    Good Submission, appreciate the read! Will read again!

  5. 5 John July 11, 2011 at 5:39 pm

    Good Submission,
    Very rarely do you get as good a set of clear views on the Web-Hosting industry. Well Done!
    appreciate the read! Will read again!

  6. 6 mkarmalay September 21, 2011 at 10:56 am

    Exceptionally Great Post…..
    Thanks for sharing…..


  1. 1 OpenSim prices drop to $10 per region – Hypergrid Business Trackback on August 25, 2010 at 11:25 pm

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