Virtualizing Cuts Web App Performance 43%

czei writes "This just-released research report, Load Testing a Virtual Web Application, looks at the effects of virtualization on a typical ASP Web application, using VMWare on Linux to host a Windows OS and IIS web server. While virtualizing the server made it easier to manage, the number of users the virtualized Web app could handle dropped by 43%. The article also shows interesting graphs of how hyper-threading affected the performance of IIS." The report urges readers to take this research as a data point. No optimization was done on host or guest OS parameters.

Comments

Virtualize this

[Anonymous Coward]

That is all very well, but we all KNOW apps slow down when we run them in a VM. What difference does it make to the average n00b who wants to watch funny videos and check their email? Anyone using computers for serious numbercrunching obviously won't virtualize anyway. No big deal

Re:Virtualize this

[Fordiman]

I do like the idea of a variably sized beowulf cluster running a floating number of package (LAMP) servers. Get more clients? Add more VLAMPs. Things slowing down? Add more hardware.

You still take performance hits, but if you can scale your system by just adding cheap commodity systems, that works. Plug it in, boot it off a CD, and let the Cluster take control.

Well,

[Fordiman]

Duh.

Seriously. I don't know who gave anyone the impression that virtualization was a performance booster. Management improver? Sure. Stability insurance? Why not? But if you don't get that virtualizing your servers imposes a bit of overhead, then you're probably not paying attention.

I especially love the idea that running different types of server virtualized on the same machine is a good idea; the idea of virtualization of multiple servers is to distribute the load. If you have, say, ftpd, httpd and mysqld running as their own virtualized systems, they will all get hit *simultaneously*.

Again. Duh.

Re:Well,

[Mr. Underbridge]

Seriously. I don't know who gave anyone the impression that virtualization was a performance booster. Management improver? Sure. Stability insurance? Why not? But if you don't get that virtualizing your servers imposes a bit of overhead, then you're probably not paying attention.

Well, I think the point was that he attached an actual number to the amount of the performance hit, which is relevant. That's called research; quantifying and proving that which seems 'obvious'.

Re:Well,

[Fordiman]

Well put. But I do know a number of people in the industry that will be shocked by this, which was who I was referencing.

But really. If you've got the money for the extra hardware to maintain performance, I say go for the virtualization, if only to make yout IT guys' lives easier (happy IT is useful IT).

Re:Well,

[hey!]

Well, it's not a surprise, but it's probably worth quantifying.

Here's a question: what is more available: hardware or skilled system administrators? Obviously hardware.

Here's a common scenario: you've set up a system to provide some useful package of services. How do you let other people duplicate your success? (1) tell them what hardware they need and (2) have them install and configurethe software on their hardware. Guess which item involves the most cost in the long run?

The hardware is easy; the greatest barrier and cost is the process of installing and configuring the software. That's one place a virtual machine is worth considering in producation systems. You aren't going to use something like VMWare in one-of-a-kind production systems. You're going to use it when you need to clone the same set up over and over again. This is very attractive for application vendors, who spend huge amounts of support on installation and tracking down compatibilty conflicts.

Another application would be an IT department that has to support dozens of more or less identical servers, especially if they are frequently called upon to set up new servers. If I had a choice, I'd use Linux virtualization on a midrange or mainframe, but if those servers must be Windows servers, then I'd be looking at some kind of cluster with SAN. This is not really my area of expertise, but we're talking high end boxen for x86; if the typical server didn't need 100% of box, then I have three choices: waste server bandwidth (expensive), force groups to share servers (awkward and inflexible; what if I have to separate two groups joined at the hip?), and virtualization.

Naturally if you are virtualizing production servers, you need to scale your hardware recommendation up to account for VM overhead.

What would be very interesting is a study of the bottlenecks. If you are considering a system with certain characteristics (processor/processors, memory, storage/raid etc) and you have X dollars, where is that best spent?

Re:Well,

[jalefkowit]

if you don't get that virtualizing your servers imposes a bit of overhead, then you're probably not paying attention...

In fairness, a 43% performance hit is a bit more than "a bit". It's cutting performance nearly in half.

I agree with your overall sentiment (a virtualized system is going to be slower than the same system running on real metal, by definition) but 43% is certainly a higher figure than I would have expected.

Re:Well,

[drinkypoo]

To us, the whole point of virtualization is that we have several servers which are mostly idle at all times and completely idle at most times, and for support reasons we're not supposed to be running anything else on the same copy of windows. So we can replace five or six systems with a four-core 1U box with just a few gigabytes of memory, which will recover rack space and reduce power consumption. For anything that's actually heavily loaded, running on the hardware is probably a very good idea.

Re:Well,

[inKubus]

It's not just support reasons. A lot of MSFT products require a dedicated server because they use the Default Web Site in IIS ;) Multi-Tenancy is not an option for many even modern server products. So, virtualize the server.

Bogus Test

[Anonymous Coward]

Who uses VMWare Server in a production environment anyway? We run all of our Web services, Exchange servers and SQL databases in VMWare's Virtual Infrastructure 3. VMWare Player and Server are only ment for lab evironments and low load applications. VMWare even says as much on their website. Either this is just FUD or the author is an idiot. In other news water is wet.

Re:Bogus Test

[Sobrique]

Actually, the company I worked for 6 months back, one of the projects I was involved in was 'VMWare'. Production stuff running on on the ESX servers (which became 'virtual infrastructure') in our datacentre, as a cost effective scalable environment. Yes, we weren't getting 'uber performance' but then again, we were running 150 or so VMs on an 6 server VMWare farm.

One of the other things we prototyped and deployed was 'site services packages' - get GSX (now VMWare Server), stick it on a pair of 2U servers, and attach a storage array to both of them. Then create your 'template' fileserver, DHCP server, print server, proxy, that kind of thing and deploy them to this package. It worked very well indeed - you get a whole new order of magnitude on stability (although to be fair that's in part because we through away the crappy workstations that were doing the 'low intensity' stuff) and was extremely managable, and trivially replacable in the event of a hardware failure.

Performance? No, VMWare isn't that great on performance - whilst it's not bad, in an ideal situation, fundamentally what you are doing is introducing an overhead on your system. And probably contention too. But it's really good at efficient resource utilisation, easy manageability and maintainability.

As an experienced sysadmin, my reaction is screw performance. Let's start with reliable and scalable, and then performance just naturally follows, as does a really high grade service.

Proactive laziness is a fundamental of systems admin. Your job, is essentially to put yourself out of a job - or more specificially, free up your time to play with toys. The best way to do this is build something stable, well documented and easily maintainable. Then your day consists of interesting stuff, punctuated by the odd RTFM when something doesn't work quite right.

Re:Bogus Test

[afidel]

Here's a little spreadsheet I created to do a cost/benefit analysis for Vmware ESX. There are some assumptions built in, and it's not yet a full ROI calculator, but it gets most of the big costs. Cell A1 is the number of our "standard" systems to be compared (4GB dual cpu 2003 machines). The DL580 is 4xXeon 7120 with 32GB of ram, local RAID1 on 15k disks, dual HBA's and a dual port addon NIC. The DL585 is 2xOpteron 8220HE with 32 or 64GB of ram (the 580 with 64GB was more expensive than buying two with 32GB!) and the same equipment. The 360 is our standard build currently, dual 5110's with 4GB ram and local RAID1 and an HBA.

The interesting thing is the breakeven point for VMWare is only 12 servers, way, way below what you can put on two of those boxes. VMotion is the killer feature for me so less than 2 servers is stupid for my situation.

Re:Bogus Test

[sammy baby]

Yes: it performs much, much better.

VI3 is actually a suite of products. At the heart is VMware ESX Server, which is actually an operating system in its own right: it runs "on the metal," without having Windows or Linux installed already on the system. It also has a service console operating system which looks suspiciously like a *NIX style operating system, so you can SSH directly to the system, cd into your /vmfs directory and, say, scp disk files over the network. If you wanted to.

However, as a pretty damn safe rule of thumb, no system is going to run faster on equivalent hardware after being virtualized. In a prior job where I was often asked to provide development/test systems, I got phone calls from a lot of people who were bitten hard by the virtualization bug. Whenever someone brought up any issue having to do with infrastructure, no matter how odd or off the wall, they wanted to push virtualization as a solution. I had to explain to them that if your problem is that a web server is slow, the answer isn't to install VMWare server on it, set up two host operating systems, and say, "There! Now I have two web servers." You'd be surprised how pervasive that sort of thinking is, even among people who should patently know better.

Another useful guideline: various types of services are impacted differently by being virtualized. Generally, the best candidates for virtualization are ones that spend a lot of time idle. This is actually more common than you might think - people need a server set up for something, can't put it on a pre-existing system for security/compatibility reasons, so they go out and buy a new system which is ten times more powerful than they need. You can put a lot of these kinds of systems on a single, reasonably powerful ESX server. On the other hand, systems that heavily tax available hardware, especially I/O, are usually much harder to deal with.

Re:Bogus Test

[Bohiti]

Actually, as it's been explained to me, the ESX hypervisor itself is pure proprietary code (and small, too). The Service Console is very readily admitted to be a tweaked out RHEL (3, I believe..). Linux is used to boot, and then (magically?) transfers control of the bare metal to the hypervisor. Linux then jumps into a virtual machine, although it's not presented like a virtual machine, which creates all this confusion.

In the end, the tweaked RHEL that you interact with (ssh, scp) is not the hypervisor, but a VM with special tools that can manipulate the hypervisor.

Re:Bogus Test

[kscguru]

Not really - HP and IBM's project get 20% improvements by optimizing slow code - that is, untuned userspace applications. Take a whole system, including a kernel that multitudes of people have spent years tuning (Linux, Windows), server apps that already squeeze in as many tricks as possible (Apache), and the net gains of re-translating instructions diminish as the underlying apps already pull in more of these optimizations. Dynamo and DAISY also gloss over one crucial detail: you need a good-sized cache to store all these translations, so they're really a time/space tradeoff (more efficient in time with a cost in space efficiency).

That said, the COST of binary translation is never very high. A good BT engine gets essentially native performance (1% overhead is quite obtainable), and is limited only by the size of the translation cache.

This is VMware Server and not ESX Server

[Fuyu]

They performed the test on VMware Server not VMware ESX Server which is what most enterprises will use. VMware ESX Server runs on "bare metal", so it does not have the overhead of the host operating system.

Re:This is VMware Server and not ESX Server

[Fuyu]

Yes VMware ESX Server runs a modified version of Red Hat Linux.

According to Wikipedia, "VMware ESX Server uses a stripped-down proprietary kernel (derived from work done on Stanford University's SimOS) that replaces the Linux kernel after hardware initialization. The Service Console (also known as "COS" or as "vmnix") for ESX Server 2.x derives from a modified version of Red Hat Linux 7.2. (The Service Console for ESX Server 3.x derived from a modified version of Red Hat Enterprise Linux 3.) In general, this Service Console acts as a boot-loader for the vmkernel and provides management interfaces (CLI, webpage MUI, Remote Console). This VMware ESX hypervisor virtualization approach provides lower overhead and better control and granularity for allocating resources (CPU-time, disk-bandwidth, network-bandwidth, memory-utilization) to virtual machines. It also increases security, thus positioning VMware ESX as an enterprise-grade product."

Re:This is VMware Server and not ESX Server

[Anonymous Coward]

ESX Server still gives you a base 40% performance hit. I run a ~600 VM farm under VI3 and our performance on Apache fell from 15000 requests/s (mostly static content) to 5000. That was during a load test with one single virtual machine running on the blade. The same load test using IIS went from 13000 to 9000. Also a huge performance hit, although not quite as bad as on Linux. And before anyone says anything, I'm a linux tech and I was somewhat deprssed about the results, to our windows techs great joy.

Re:This is VMware Server and not ESX Server

[Quikah]

I think everyone is kind of looking at this the wrong way. Sure you get a performance hit, but yu are testing maximum performance. That is a situation where you wouldn't want to virtualize anyway. If the system is running at 100% utilization, then leave it alone. It is more interesting to take your servers running at 20-30% util (if that, how many idle server do YOU have?), and cram them all into a couple of boxes. You most likely WON'T see a perfromance drop because there was so much headroom on the system already. Virtualization struggles at the max utilization case, but then that is not the case that it is really meant for.

This has been my experience too

[SCHecklerX]

Linux under VMWare's network performance is pretty bad. An interesting visual confirmation is to use an ssh shell and watch the lag. That may just be the broadcom chips in the servers the company I was working for used, though. Guest OSes are fine for some low traffic stuff that only a few people will be using, and is definitely the way to go in the test lab; but I wouldn't use this configuration as a company's primary reverse proxy or mail solution.

That said,
I use a windows vmware session under linux for those times I have no choice, and it works just fine network-wise as a workstation.

Re:This has been my experience too

[Thundersnatch]

But then again, I've got 6 Gigabit NICS load balanced on a Gigabit backplane with the VMs all running on an independent SAS array on a quad processor hyperthreaded box with 32 GB of RAM. But perhaps your box has equally as good specs, I don't know.

Oh yeah? Well my Johnson is longer than yours, and my son can beat up your son.

Sounds about right

[Anonymous Coward]

My first attempt at virtualization was last September with VMWare Server. During testing everything seemed fine. When everything was using it, performance was awful. Everything crawled. I ended up doing an all-nighter to move everything back to a regular server. Note, I wasn't overloading things. There was only one VM on the host. The memory was fixed, not paged to a disk like it is by default. The hard drive was preallocated. My intention for virtualization was to make things easier to manage.

That's when I started experimenting with Xen. This time I put the test under a very high load, and it seemed to handle everything well. I deployed it in October and so far there hasn't been a single performance issue.

I'm now totally addicted to Xen. I create Vms all the time, have split up services into different VMs (ie, when cups crashes it no longer takes out the copy of samba that handles logins, damn I hate cups). So far, no performance issues at all.

Re:VMware Server 1.0.1???

[Fuyu]

VMware Server 1.0.1 is their free virtualization product that runs on a host OS (linux or Windows). Most enterprises will use VMware ESX Server 3 with the VMware Virtual Infrastructure 3 series of products as it runs on "bare metal" and does not have the overhead of the host OS.

single data point is correct

[Visaris]

Dell Poweredge SC1420 with dual Xeon 2.8GHz processors

While I can't seem to find all the information on the SC1420, it appears as though this product uses processors from the Prescott generation of Intel CPUs. Some chips from this group support "Vanderpool", Intel's hardware virtualization solution, but not all do. The presence or absence of this feature could greatly impact the performance penalty faced by operating a virtualized computing environment. Further, Intel's new Core2 based CPUs feature a hardware virtualization implementation which may have vastly different performance characteristics. AMD's K8 family supports hardware virtualization as well. I'm excited about their new line of CPUs based on the K10 (Barcelona) core, which feature "NestedPageTables," which are supposed to greatly reduce overhead by doing memory translations in hardware instead of in software by the hypervisor.

All I'm really trying to say is that this article really is only a single data point. I wouldn't let their results influence your overall view of virtualization in any way...

Re:single data point is correct

[TheRaven64]

The biggest overhead from most forms of virtualisation is from emulated devices. If you have loads of money, you can give it to IBM and get some hardware with virtualisation-aware network and block device controllers. Then you get good performance. Alternatively, you can use paravirtualised device drivers. Xen supports this by default, and I think KVM does now for networks. Not sure about VMWare.

With paravirtualised devices, or devices that are virtualisation-aware, a VM can be within 10% of the performance of a real machine quite easily. Without I'm surprised they even got to 57% of native performance for web applications.

Re:single data point is correct

[Natales]

VMware's vmxnet driver is paravirtualized and it does provide better performance than the traditional pcnet32 virtual device driver, which operates 100% on software to maintain compatibility with other OSs.

Regarding paravirtualization, it's already known that the new VMware Workstation 6 (currently in beta) and presumably the next version of VMware Server, will support VMware's version of paravirtualization called VMI, which was officially accepted as part of the stock Linux kernel starting on 2.6.21. This may help boosting the performance of Linux-based VMs significantly, and unlike the Xen version, it will boot a single kernel image, regardless of the physical or virtual underlying hardware platform.

Re:Not a trusted source

[dagenum]

The hyperthreaded capacity was actually 390 so a 3% gain.

Pointless test?

[geoff lane]

Come on! You run virtualised web servers because 99.9% of all web servers are idle at any given time. So you put 100 on a server. The customer doesn't see any worse performance with their 3 hits a week page and the ISP makes more money/server.

Re:Pointless test?

[LurkerXXX]

No it's not insane. Lots of customers want full root access on their systems so they can install whatever they want (different database or other servers, or even alternate OS's). Virtualization is the only way to go for that.

Re:Pointless test?

[Albanach]

It's not insane if people want different solutions or even want their own server. With virtualisation, a host can offer multiple php versions. You can avoid all the security problems where one script running as the webserver can read any other file accessible to the web server.

You can also get better management control of resources, preventing one site from eating up all available resources on the box.

That's not to say there aren't a million good reasons to use virtual servers in apache, just to point out that virtualising web hosts is not, by definition, a daft idea.

Re:Pointless test?

[GiMP]

AssignUserId only works with the perchild MPM, which has the following caveat: "This module is not functional. Development of this module is not complete and is not currently active. Do not use perchild unless you are a programmer willing to help fix it."

Thus, AssignUserId should NOT be used. SuExec can be used, of course, but that has its own limitations.

Personally, I give users their own Apache processes on their own port (>1024) and use a reverse proxy. I make a living on it.

Re:Pointless test?

[Just Some Guy]

You run virtualised web servers because 99.9% of all web servers are idle at any given time. So you put 100 on a server.

If you have a real need to run 100 separate Apache instances, then you'll want something much higher-level than VMWare. For us, that would be a FreeBSD jail, where each instance would get its own chrooted home directory and IP address. That way, you're not allocating resources to 100 little-used OS images; each shares from the same memory and hard drive pool. Jails are slightly limited in that I'd like a way to limit CPU and memory allocation, but in practical application this really works very well today.

Re:Pointless test?

[Just Some Guy]

The chroot-jail based hosting system I used had a number of problematic limitations: I couldn't install any software that needed to run as root (e.g. to open ports below 1024), I couldn't change configuration of a variety of services that would open security problems for the hosting provider (e.g. the mail server, I think they were using exim), users running processes on the same server that consumed too much CPU and or memory had too much negative impact on my server's performance.

Of those, only the last is relevant to FreeBSD jail setups. If I created a jail for you and gave you root, you would be root, full stop. The only things you could do would be install your own kernel (since only one kernel - that of the host OS - is running). We use them to virtualize multiple distinct systems on the same hardware, with the idea that the mailserver always runs under a light load and doesn't interfere with the database server hosted on the same machine.

There's a decent Wikipedia article on the subject, even if it kind of comes across like an advertisement. In short, it sounds like your hosting provider ran a bad server. Don't extrapolate their incompetence to the general state of the art.

VMWare ESX server *can* share memory and free disk space between instances. Multiple instances can even have the same page of physical memory mapped into them, so running multiple identical servers doesn't actually take more memory than it does on a single instance (although there are overheads).

Assuming a strategy like copy-on-write, I can understand how two instances started from the same configuration could begin with most of their memory shared. However, it seems like that would eventually become a tiny percentage of their actual address space as processes start and die, allocate memory and free it, etc. I mean, to the best of my knowledge, when Unix fork()s a process, it doesn't keep track of when it can later re-merge the address space of the parent and child. They may start as identical copies, but pretty soon their data segments will be completely different. In the case where each process is actually a virtualized system where the data segment is hugely bigger than the shared code, I'd think that would happen pretty quickly.

Bad data, bad setup

[duncanFrance]

There's quite a lot wrong with their setup.

1) As others have pointed out, they should be running on ESX to get best performance.
2) Physical machine was a dual-proc. How many processors did they assign to the VM?
3) Physical machine had 2GB memory. They assigned 2GB to the VM!! Vmware will take 256MB of this
for itself, so that 2GB visible to Windows will be being swapped.
4) How many disks did the physical machine have, and what was on them?
If e.g. the physical machine had two disks, the VM should have been given two disk files, with each file being placed on a different physical spindle.

You get the picture.

holy cow am I a nerd

[thegnu]

I do like the idea of a variably sized beowulf cluster running a floating number of package (LAMP) servers. Get more clients? Add more VLAMPs. Things slowing down? Add more hardware.

I started getting aroused as I read your post. This is highly disturbing.

"Duh!" moment

[Thumper_SVX]

I agree with many of the commentators here that this is pretty obvious. We use virtualization a lot, but also realize its limitations. For example, we don't run SQL or anything heavily transaction or I/O bound. CPU utilization is usually not a problem; virtual machines perform as well as their physical counterparts in most instances unless you have a lot of CPU intensive virtual machines running.

Web servers are mostly memory and CPU bound which would give one the impression that they would be great candidates for virtualization. However, VMWare Server is not the solution; network I/O is not good on Server. Typically your results would be maybe 75% of the actual physical speed on a "passthrough", less on a NAT. It depends a lot on how your network is set up, not to mention the abilities of the physical machine.

The best solution is Virtual Infrastructure (used to be ESX). That product tackles most of the failings of VMWare server and fixes them. The only exception is that I still wouldn't run anything I/O heavy on VI. SQL's a no-no. Also, if you're not getting the performance from a single web server that you expect, you can easily throw up more web servers. Now, obviously you might get into M$ licensing issues, but that's why you run your web services on Apache :D

Fast Virtualization: Xen, KVM, Virtuozzo, GSX, ESX

[dvdan]

For speed, the newer virtualization tools KVM, Xen, and Virtuozzo are presently substantially ahead of the present incarnation of VMWare. KVM requires the new "hardware virtualization" CPU's from Intel and AMD which must be mentioned here, since they represent a major industry recognition of the value of virtualization. This article seems to be giving people the impression that performance of VMWare Server is indicative of virtualization tools in general, and that all virtualization tools slow down hosted virtual machines dramatically. This is simply false. I know hosting providers running 50 virtual servers on a single dual CPU box with thousands and thousands of users, which would simply not work if all virtualization tools had a 43% hit per instance. Another key matter here is that the author fails to mention (or realize?) VMWare Server is crippleware. VMWare states explicitly not to use VMWare Server for anything other than testing because it does not have the performance or feature set of their full blown ESX and GSX servers. Also, while VMWare may be the oldest and arguably most mature virtualization suite, it is certainly not the fastest.

These results are pretty much as expected

[Sangui5]

It isn't surprising that VMWare would be bad at a web-app workload. See the original paper on Xen:

http://www.cl.cam.ac.uk/research/srg/netos/papers/ 2003-xensosp.pdf

Top of page 9 has a chart comparing native Linux, Xen, VMWare, and UML for different workloads. They show VMWare degrading performance by over 70% for SPECWEB 99.

Web applications are OS intensive; while VMWare is quite good at pure CPU-bound tasks, it has to perform a lot of emulation whenever you are running inside the OS. So it will stink at anything with lots of small IO, lots of metadata operations, or lots of process creation/switching. For example, VMWare shows a whopping 90% slowdown for OLTP database workloads, according to the Xen paper, and it really isn't surprising. The OS microbenchmarks in the above paper (page 10) show that VMWare has abysmal performance for things like fork(), exec(), mmap(), page faults, and context switches.

Basically, Xen doesn't have to emulate the OS, because they make modifications to the OS. VMWare does dynamic binary rewriting (think fancy emulation) to run an unmodified OS; they therefore pay through the nose in performance overhead for OS-intensive workloads.

IIS can't be paravirtualized

[tepples]

Not to mention the fact that paravirtualization as well as hardware assisted virtualization like Xen offers (and later Longhorn) really cut the performance issues WAY the hell down. Paravirtualization also requires a free software OS kernel, and IIS-only web applications are do not yet run on any free software kernel. (ReactOS is nowhere near mature enough.) Any virtualization also requires more OS licenses and higher-class, more expensive OS licenses. Or do you claim that all web app developers should drop IIS-only frameworks immediately, and all enterprises that rely on IIS-only web applications should drop their mission-critical IIS-only web applications immediately?

Re:IIS can't be paravirtualized

[Joe U]

I do not understand people that make mission-critical IIS-only webapplications, isnt that just stupid?

No.

It's no different from focusing on any other major corporate product. ASP.NET isn't going away anytime soon and it's not going to fall over anytime soon.

It's run by Microsoft. Despite what the ranting morons around here think, Microsoft is not going away, IIS is not an insecure mess and it's actually a really good platform for web applications.

Now, that being said, use the best tool for the job, otherwise you're just stupid.

This is comparing single to dual proc

[sheldon]

They state in the test that the servers are dual proc servers.

VMWare Server, the free edition only emulates a single processor environment for your virtualized host.

VMWare ESX or whatever they are calling the expensive thing today, has the ability to give your virtualized host multiple processors.

So it's not surprising that it could only handle half the load, it only had half the processors.

We don't do virtualization for heavy use environments. We do it because different business groups don't want to share servers... that is, they can't agree on maintenance windows, etc.

But the conclusions don't match the research

[g2devi]

Th key thing to not is that their tests don't substantiate their conclusion:
> These results indicate that a virtualized server running a typical web application may experience
> a 43% loss of total capacity when compared to a native server running on equivalent hardware.

This may lead to people believing that virtualiz]ation just isn't worth the advantages. The key problem is that there are several virtualization schemes. Off the top of my head, I can list:
        * Xen
        * KVM
        * Linux-VServer
        * OpenVZ
        * User Mode Linux
        * lguest
Each has it's pros and cons in terms of overhead, maintenance, and performance. Generalizing based on one VMWare configuration, is just plain foolish.

Let's not forget the old chroot approach that gives you 90% of the advantages of virtualizing web servers with few of the disadvantages.

The key thing to do is to pick the right technique for the right task.