What is the biggest difference between KVM and vSphere?

KVM can take full advantage of the operating system where it is hosted.

I have read a lot of valid arguments, and, unfortunately a lot of flawed arguments too .
What I will write here is based on my personal experience , I run a half dozen Enterprise level vitualized environments :
For the perspective of most of my customers, the main difference are the ability to audit the code of KVM ( witch are Open Source ) and a lack of it in VMWare .
VMWare is a black box, no one knows what happens inside of it, what are done with the VMs that are running over it .
Insted of it, with KVM, you know exactly what is happening . You know that KVM are not sending sensitive information about your VMs, or statistics about your environment to the vendor .
In second place comes the TCO :
KVM are not completely "free", you need some tools to manage it, but it is WAY cheaper compared to VMWare .
Lot of vendors says that "VMWare runs the world" , really ?
Amazon runs over XEN, Google and Facebook runs over KVM, and Microsoft runs over Hiper-V, sum all 4 and you will have more than a half of the big players on earth, so, from where comes that statement ?!?
About performance, nowadays there are no big difference between all the systems, technology blurred the lines between Type 1 and Type 2 Virtualization approaches .
Open source management systems ( Like Proxmox used by Facebook ) leveled the line between Commercial and non-commercial tools .
Yes, there are some scenarios that VMWare makes sense, buts the decision on witch are better for a particular user case goes down to the details .
Think about that before spend your budget of 2 or 3 years in one tool .

Fábio Rabelo

I'd say the main difference that sticks out like a sore thump is the KVM is Opens source and VMware vSphere isn't. VMware is indeed the Rolls Royce of virtualization but doesn't come cheap. One has to have deeper pockets to access the finer enhanced features of the vSphere packages. KVM on the other, is also a stable Hypervisor and very popular with Linux inclined techs and gurus. Personally i'd encourage one to take the VMware vSphere route because of the solid global support of the product, the additional virtualization feature rich set offerings like vSAN & NSX and ease of use from the onset.

If you run applications that are not relying on infra you can run that on KVM. VSphere offers more functionallity to support the application from a infra perspectve. Most traditional enterprise apps I would not run on KVM, also taking into account the support you may need, but apps build for OStack or OShift should run fine.
From a cost perspective VMware is mire expensive to buy, but from a TCO perspective that may flip depending on the workloads you are running. Don’t get blinded by SW being ‘free’. It never is, weather you have to buy support, or arrange / deliver it yourself, you have to give back to the open community, and may need more tiols or scripts if you need to cover functionality you need that is not Standard avalable in KVM, again depending on your workloads and their requirements

KVM is Hypervisor and vSphere is platform but Ovirt is platform with KVM.
The big difference it's cost but vMware is leader on Virtualization.

KVM is a simple and OpenStack-preferred virtual machine manager. vSphere is a different beast altogether, as it is expensive and ridden with lots of add-ons for VM infrastructure provisioning.

One answer to your question will be a company that can afford and wants to have a stable and long-term VM infrastructure can consider VMWare, as KVM is considered as a bare-bone VM manager.

The actual comparison should be between VMWare and OpenStack, as one is paid and one is free to deploy. The deployment for OpenStack can be a little trial and error as it is free and modular, and VMWare is fully-packaged, and it is easier for you to deploy, but at a cost that is calculated by per host.

Service Virtualization has nothing to do with KVM and vSphere. KVM and vSphere are tools/environments to virtualize systems/servers, not services.

Service Virtualization is used to virtualize a Web service or a Message-based service. KVM and vSphere are used to virtualize Linux or Windows systems.

So, I assume you got confused by the very similar name of both. If I misunderstood the questions, please let me know. I am happy to help.

BTW, you can run Service Virtualization on virtualized Linux and Windows boxes.

There are many of comparisons of KVM and vSphere on the internet, see, for instance, community.spiceworks.com

Hope that helps.

KVM Doesn't have any Dynamic ressource allocation like VMware (DRS). support is not the same you can have a community support or you can get Redhat RHV for entreprise paying support. With VMware vsphere you will get one yo three years support with your purchase.
Don't forget to look to other alternative like acropolis from Nutanix, XEN, RHV and Hyper-V also. Define your need and chose the product that will fit best your need. Don't forget there is also a free version of VMware esxi with no central management available.
Personnaly for a single host i ll go to free ESXi or Hyper-V if my company is using windows. For linux i ll go to acropolis or ESXi.
If i want to do some openstack i ll go with KVM or ESXi with Vmware integrated openstack.
For a small datacenter or big VMware offer a lot of features and hyper-v a little less. If you have a lot of windows licence Hyper-v will be cheaper than vmware. VMware is robust and can be scale up and out easily.

Vmware has more integration with other 3rd party product than KVM. Backup software for instance.

KVM and Vsphere are Type 1 hypervisor meaning they run directly on the system hardware
KVM (or Kernel-Based Virtual Machine) is a Linux-based type-1 hypervisor that runs on most Linux operating systems including Ubuntu, Debian, SUSE, and Red Hat Enterprise Linux.

The way I read this question is which is the better platform on which to build Service Virtualization. If that is the case, then the next question is if you expect a 'productized' offering that can be expected to run more-or-less out of the box. If that is the case, then VMware. If you expect to also run enterprise workloads, the likewise VMware. If you think things like backup and DR are reasonable expectations for your environment, again VMware.

OpenStack was intended from the beginning to perform one task: spin up a bunch of VMs to crunch some numbers, then make those VMs go away when those workloads were complete. Things like availability, backups, geo-diversity, stability were minor concerns, because if it broke ... spin up a new instance and rerun the job. This is worlds away architecturally, functionally, and operationally, from the Enterprise computing that VMware was intended to support. OpenStack VMs were fungible, and their data ephemeral, transient, and not presistent. Unfortunately, most business and enterprise applications, and specifically their data are necessarily very persistent.

There is a wonderful video on YouTube of a talk given at an OpenStack conference by one of the original OpenStack authors that details this, and the things they would have done differently if they had known what they know now.

Biggest difference is ofcourse license model - KVM is free, open source, vsphere not. Support model is therefore also different - community&companies (eg. RHAT) versus company (vmware). Both can virtualize workloads pretty nicely. Both have GUI available. Whole operations management for Enterprise with many, different CIs are most propably easier to manage with vmware solutions which have many plug-ins and supported by manufacturers too but being more expensive than pure KVM and open-source solutions where admins most propably need some knowledge of linux, scripting etc.. Take a look of Containers/Kubernettes for your workloads. That might be even better solution for your virtualization need.

KVM VS vSphere biggest difference is Support
KVM is open source Virtualization software, Cannot support Enterprise Service
KVM is free, If you want support KVM then only yourself support or community support
vSphere is VMware Virtualization software, You Can support Enterprise Service(VMware)
vSphere is not free, if you want Virtualization service by vSphere for Customer is ok
but KVM have problem about Support
KVM base Enterprise software is RHV(Red Hat Virtualization), RHV support by RedHat
My recommend is vSphere or RHV
but I'm not recommend KVM for company service

Don't bother with either. Move your workloads to the cloud

vMware is much closer to virtual, as opposed to simple hardware swapping.

vSphere is the best option in my opinion, if you have enough budget to buy it. But also vSphere is more complete and easy to use.
Options like KVM of course are free but you have to be ready to wait help or sopport from the KVM community, in case of VMware you have the support from a paid support so you will have a response. Another aspect you can consider is the compatibility with software from other manufacturers, for example: You can donwload a ready applice from F5 or CISCO to deploy in your VMware plataform and just configure what you need.

Easy, obviously the software architecture but more importtant the cost for premium functionality.

I always recommend if you are in the position you don't need support from the brand, choose any free software solution.

I think everything has been said. You already have a lot of opinions, and I don't want to repeat them.
But in the end, it depends on two things:
Your budget and your needs.
I agree with Byungwoong Shin ... If you can, go with ESXi / vSphere, is more reliable

KVm is a type 2 Hypervisor. It runs as an application inside a full fledged operating system. Thus the hypervisor layer is not as thin as in a dedicated type 1 hypervisor like Vsphere ESXi. Given that it does seem to be comparatively lightweight comapred to other such technologies like virtualbox etc

Each solution provides various benefits depending on the situation. If a company were seeking an open-source solution that could integrate into an existing API, they would most likely benefit from KVM's ability to be scripted. VMware is a good out-of-box proprietary solution that provides front-end tools for to manage the VM infrastructure. It is unfortunately less forgiving than KVM in it's ability to be scripted.

I am not sure this questions should be categorized under SERVICE Virtualization... since these two solutions are in reality SERVER Virtualization solutions.

Those solutions virtualize the actual hardware the software is running on. Service Virtualization will virtualize the call a system under test (SUT) is receiving, instead of getting a response from the “real thing” it gets a virtual service response, that acts and behaves just like the real thing.

Essentially service virtualization can be said to be a smarter and more versatile way of mocking and stubbing.

Those are both Virtual Machine software... or Server Virtualization solutions... NOT Service Virtualization.

Those solutions virtualize the actual hardware the software is running on. Service Virtualization will virtualize the call a system under test (SUT) is receiving, instead of getting a response from the “real thing” it gets a virtual service response, that acts, behaves just like the real thing. Essentially service virtualization can be said to be an extremely smarter and more versatile way of mocking and stubbing.

Hope that answers it...

You want Alan Baptista on this one.

Nowadays, differences between hypervisors are not bond to capacity or performance things. tie-breakers are : Management Tools, Compatibility and integration with other solutions, automation and much more. if your are going to use a single host with a local storage and don know something like that then I think you don need to worry too much. But for example if we are talking about an SDDC , VDI then it is completely different. But I the most important factors to consider from my point of view are: 1-what are you good at 2-money :D
Good Luck

A big compant should consider Parasoft and CA

vSphere is more expensive but has an really nice gui and support for lots of different management software. KVM on the other hand is usable as opensource software but comes with less easy to use management software.

Those are the biggest changes, but also supporting of features like hot migrate and hot-add of virtual hardware is far better supported on vmare. Things can be done in KVM but are much harder to learn and you must understand linux scripting to be able to manage an KVM system in full.

No experience with KVM. I am of the opinion that a company with millions in revenue should consider what does it cost to save a few dollars. Availability of administration, ability to get rapid support for a mainstay product and reliability of the company supporting must be considered, not just the licensing cost. Is VMware free, No? Is KVM free? Yes. If free always cheaper? Definitely not. If your company depends on your IT and your cost of being down could be measured in the ten of thousands of dollars per hour, what is free worth? just a question to be considered before getting "free" stuff.