KVM vs XenServer



  • We're beginning to test KVM a bit here to compare it to XS, but I was curious if there were reasons that you all aware of to choose one over the other.


  • Service Provider

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices. XS is the stack, so you are limited to the choices in that stack. XS is good and has a lot of good things baked in and some good add ons, added on but it also removes some flexibility, makes some dumb choices and slows down development (compared to straight Xen.)

    KVM is definitely getting way more attention and is gaining on Xen all of the time. Xen has some cool tech coming down the pike that will potentially leapfrog it over KVM in terms of Linux virtualization performance, but right now KVM has the lead in a small way with Linux and a large way with Windows where KVM has always focused.



  • @scottalanmiller said in KVM vs XenServer:

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices. XS is the stack, so you are limited to the choices in that stack. XS is good and has a lot of good things baked in and some good add ons, added on but it also removes some flexibility, makes some dumb choices and slows down development (compared to straight Xen.)

    KVM is definitely getting way more attention and is gaining on Xen all of the time. Xen has some cool tech coming down the pike that will potentially leapfrog it over KVM in terms of Linux virtualization performance, but right now KVM has the lead in a small way with Linux and a large way with Windows where KVM has always focused.

    So in performance they have rough parity with Linux workloads, and KVM currently has the edge in Windows? It seems odd to me that KVM has focused on Windows. I would've thought the other way around.



  • @scottalanmiller said in KVM vs XenServer:

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices.

    Can you give me some examples of things that would go in that stack? I'm just starting learning about KVM as a category.


  • Service Provider

    @Kelly said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices. XS is the stack, so you are limited to the choices in that stack. XS is good and has a lot of good things baked in and some good add ons, added on but it also removes some flexibility, makes some dumb choices and slows down development (compared to straight Xen.)

    KVM is definitely getting way more attention and is gaining on Xen all of the time. Xen has some cool tech coming down the pike that will potentially leapfrog it over KVM in terms of Linux virtualization performance, but right now KVM has the lead in a small way with Linux and a large way with Windows where KVM has always focused.

    So in performance they have rough parity with Linux workloads, and KVM currently has the edge in Windows? It seems odd to me that KVM has focused on Windows. I would've thought the other way around.

    Basically Xen owned the Linux performance space by doing PV so KVM would have to have reinvented the wheel just to compete, but they were able to go after non-PV workloads (like Windows) pretty heavily to differentiate themselves. So mostly just market pressure.


  • Service Provider

    @Kelly said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices.

    Can you give me some examples of things that would go in that stack? I'm just starting learning about KVM as a category.

    Like your management layer or storage layer. Like if you want DRBD or Starwind, you bring your own. Or if you want a GUI or whatever on top.



  • @scottalanmiller said in KVM vs XenServer:

    @Kelly said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices. XS is the stack, so you are limited to the choices in that stack. XS is good and has a lot of good things baked in and some good add ons, added on but it also removes some flexibility, makes some dumb choices and slows down development (compared to straight Xen.)

    KVM is definitely getting way more attention and is gaining on Xen all of the time. Xen has some cool tech coming down the pike that will potentially leapfrog it over KVM in terms of Linux virtualization performance, but right now KVM has the lead in a small way with Linux and a large way with Windows where KVM has always focused.

    So in performance they have rough parity with Linux workloads, and KVM currently has the edge in Windows? It seems odd to me that KVM has focused on Windows. I would've thought the other way around.

    Basically Xen owned the Linux performance space by doing PV so KVM would have to have reinvented the wheel just to compete, but they were able to go after non-PV workloads (like Windows) pretty heavily to differentiate themselves. So mostly just market pressure.

    How much of a Linux performance difference nowadays between Xen and KVM? Boot up time, IOPS, etc...


  • Service Provider

    @black3dynamite said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    @Kelly said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices. XS is the stack, so you are limited to the choices in that stack. XS is good and has a lot of good things baked in and some good add ons, added on but it also removes some flexibility, makes some dumb choices and slows down development (compared to straight Xen.)

    KVM is definitely getting way more attention and is gaining on Xen all of the time. Xen has some cool tech coming down the pike that will potentially leapfrog it over KVM in terms of Linux virtualization performance, but right now KVM has the lead in a small way with Linux and a large way with Windows where KVM has always focused.

    So in performance they have rough parity with Linux workloads, and KVM currently has the edge in Windows? It seems odd to me that KVM has focused on Windows. I would've thought the other way around.

    Basically Xen owned the Linux performance space by doing PV so KVM would have to have reinvented the wheel just to compete, but they were able to go after non-PV workloads (like Windows) pretty heavily to differentiate themselves. So mostly just market pressure.

    How much of a Linux performance difference nowadays between Xen and KVM? Boot up time, IOPS, etc...

    KVM has a slight edge right now. But it is expected to be lost in the future.



  • @scottalanmiller said in KVM vs XenServer:

    @black3dynamite said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    @Kelly said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices. XS is the stack, so you are limited to the choices in that stack. XS is good and has a lot of good things baked in and some good add ons, added on but it also removes some flexibility, makes some dumb choices and slows down development (compared to straight Xen.)

    KVM is definitely getting way more attention and is gaining on Xen all of the time. Xen has some cool tech coming down the pike that will potentially leapfrog it over KVM in terms of Linux virtualization performance, but right now KVM has the lead in a small way with Linux and a large way with Windows where KVM has always focused.

    So in performance they have rough parity with Linux workloads, and KVM currently has the edge in Windows? It seems odd to me that KVM has focused on Windows. I would've thought the other way around.

    Basically Xen owned the Linux performance space by doing PV so KVM would have to have reinvented the wheel just to compete, but they were able to go after non-PV workloads (like Windows) pretty heavily to differentiate themselves. So mostly just market pressure.

    How much of a Linux performance difference nowadays between Xen and KVM? Boot up time, IOPS, etc...

    KVM has a slight edge right now. But it is expected to be lost in the future.

    Lost in the future from XenServer or Xen or Both?


  • Service Provider

    @black3dynamite said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    @black3dynamite said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    @Kelly said in KVM vs XenServer:

    @scottalanmiller said in KVM vs XenServer:

    Well, flexibility is a big one. KVM is just the hypervisor itself, so you are building out your own ecosystem choices. XS is the stack, so you are limited to the choices in that stack. XS is good and has a lot of good things baked in and some good add ons, added on but it also removes some flexibility, makes some dumb choices and slows down development (compared to straight Xen.)

    KVM is definitely getting way more attention and is gaining on Xen all of the time. Xen has some cool tech coming down the pike that will potentially leapfrog it over KVM in terms of Linux virtualization performance, but right now KVM has the lead in a small way with Linux and a large way with Windows where KVM has always focused.

    So in performance they have rough parity with Linux workloads, and KVM currently has the edge in Windows? It seems odd to me that KVM has focused on Windows. I would've thought the other way around.

    Basically Xen owned the Linux performance space by doing PV so KVM would have to have reinvented the wheel just to compete, but they were able to go after non-PV workloads (like Windows) pretty heavily to differentiate themselves. So mostly just market pressure.

    How much of a Linux performance difference nowadays between Xen and KVM? Boot up time, IOPS, etc...

    KVM has a slight edge right now. But it is expected to be lost in the future.

    Lost in the future from XenServer or Xen or Both?

    Xen for sure. XenServer famously strips the power of Xen out, so who knows.


  • Service Provider

    Like XenServer removed support for DRBD and Fault Tolernace. Argh



  • It's expected that the next incarnation of Xen will use the PVH2 virtualization mode with Linux guests, bringing back some of the PV advantage.
    XenServer is pretty limited but the XAPI are solid.

    KVM performs very well, has less hardware limitations than XS and can be used on any Linux installation without fancy modding.
    Plain Xen is much harder than both XS and KVM of course, many stuff like VGA passthrough of the dom0 and networking are completely up to the user.

    The libvirt stack (that can be used with both KVM and plain Xen) is very mature and has plenty of features. I really like the automatic installation of the guests (virt-builder) and the various guest os inspection tools.



  • @Francesco-Provino We need a super-duper fancy looking web gui to manage KVM.

    How come there is nothing like ProxMox or XOA for KVM?
    I guess ProxMox is KVM!



  • @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino We need a super-duper fancy looking web gui to manage KVM.

    How come there is nothing like ProxMox or XOA for KVM?
    I guess ProxMox is KVM!

    Use oVirt if you need a web gui. Virt-manager is fine for 99% of use cases and works over ssh.

    Why do you NEED a gui for that? I found the libvirt toolstack very easy to use, the docs are good, virsh is your friend.

    I use the guy only for console access stuff, anything can be done via cli in an easier and quicker way than the grafical one.



  • @Francesco-Provino Have you used oVirt?


  • Service Provider

    @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino We need a super-duper fancy looking web gui to manage KVM.

    How come there is nothing like ProxMox or XOA for KVM?
    I guess ProxMox is KVM!

    Scale? Nutanix?

    KVM has loads of them. Just approached in a different way.



  • @scottalanmiller said in KVM vs XenServer:

    @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino We need a super-duper fancy looking web gui to manage KVM.

    How come there is nothing like ProxMox or XOA for KVM?
    I guess ProxMox is KVM!

    Scale? Nutanix?

    KVM has loads of them. Just approached in a different way.

    I meant KVM you can install & configure with your own hardware!



  • @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino Have you used oVirt?

    I've used it in my home lab. It was slow. Took a while to clone. Interface was a little slow. KVM on CentOS 7 I can fully clone my template and start the clone in around 3-4 seconds.



  • @stacksofplates said in KVM vs XenServer:

    @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino Have you used oVirt?

    I've used it in my home lab. It was slow. Took a while to clone. Interface was a little slow. KVM on CentOS 7 I can fully clone my template and start the clone in around 3-4 seconds.

    Was it slow due to your hardware not being capable?

    oVirt is Red Hat's virtualization management platform & it is supposed to be capable?



  • @FATeknollogee said in KVM vs XenServer:

    @stacksofplates said in KVM vs XenServer:

    @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino Have you used oVirt?

    I've used it in my home lab. It was slow. Took a while to clone. Interface was a little slow. KVM on CentOS 7 I can fully clone my template and start the clone in around 3-4 seconds.

    Was it slow due to your hardware not being capable?

    oVirt is Red Hat's virtualization management platform & it is supposed to be capable?

    I did do the all in one install but it has 96GB RAM and 8 cores (16 vCPUs) and 10K SAS drives. I'd hope it would run decently well on that.



  • @stacksofplates said in KVM vs XenServer:

    @FATeknollogee said in KVM vs XenServer:

    @stacksofplates said in KVM vs XenServer:

    @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino Have you used oVirt?

    I've used it in my home lab. It was slow. Took a while to clone. Interface was a little slow. KVM on CentOS 7 I can fully clone my template and start the clone in around 3-4 seconds.

    Was it slow due to your hardware not being capable?

    oVirt is Red Hat's virtualization management platform & it is supposed to be capable?

    I did do the all in one install but it has 96GB RAM and 8 cores (16 vCPUs) and 10K SAS drives. I'd hope it would run decently well on that.

    I thought the all in one is only available via their live cd version just to get an idea about it? Setting up a separate host for the engine and the other for the node works better.



  • @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino Have you used oVirt?

    The setup is complicated (on purpose?) and the interface is no that great, but it works. My last experience with oVirt was in 2016/03, maybe now could be much better. But a great cli cannot be beaten…
    IMHO most of the people think they need a gui control panel because of the "VMware cult": nice GUI client, cumbersome CLI.
    PowerCLI is usable, but not for interactive use. Virsh (for KVM) is simply great.



  • @scottalanmiller said in KVM vs XenServer:

    @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino We need a super-duper fancy looking web gui to manage KVM.

    How come there is nothing like ProxMox or XOA for KVM?
    I guess ProxMox is KVM!

    Scale? Nutanix?

    KVM has loads of them. Just approached in a different way.

    With this solutions you throw away some of the main advantages of KVM:

    • Completely FLOSS. No license issue in any way, no cost, ever. As many spare hosts as you want;
    • Every feature of the hypervisor is exploitable;
    • It's not dependent on a particular distro, vendor, product;
    • It's a core project developed by the biggest player in the OSS space, so no risk of abandonment, very high quality of the code etc.


  • I think that the only thing I truly miss in KVM is not a fancy GUI, but instead a stateless host OS 'a la XenServer/ESXi' that I can safely deploy to a usb drive. Something like CentOS atomic host should be good, but focused on KVM instead of Docker.



  • @black3dynamite said in KVM vs XenServer:

    @stacksofplates said in KVM vs XenServer:

    @FATeknollogee said in KVM vs XenServer:

    @stacksofplates said in KVM vs XenServer:

    @FATeknollogee said in KVM vs XenServer:

    @Francesco-Provino Have you used oVirt?

    I've used it in my home lab. It was slow. Took a while to clone. Interface was a little slow. KVM on CentOS 7 I can fully clone my template and start the clone in around 3-4 seconds.

    Was it slow due to your hardware not being capable?

    oVirt is Red Hat's virtualization management platform & it is supposed to be capable?

    I did do the all in one install but it has 96GB RAM and 8 cores (16 vCPUs) and 10K SAS drives. I'd hope it would run decently well on that.

    I thought the all in one is only available via their live cd version just to get an idea about it? Setting up a separate host for the engine and the other for the node works better.

    Even so it shouldn't perform that badly. There isn't anything really changing that much. Cloning a VM doesn't take much resources.



  • @Francesco-Provino said in KVM vs XenServer:

    I think that the only thing I truly miss in KVM is not a fancy GUI, but instead a stateless host OS 'a la XenServer/ESXi' that I can safely deploy to a usb drive. Something like CentOS atomic host should be good, but focused on KVM instead of Docker.

    You should be able to do a USB install and ship the logs off to somewhere else. Then just mount your disks/volume for the guests.

    I've been thinking of trying that but been too busy/lazy.



  • @stacksofplates said in KVM vs XenServer:

    @Francesco-Provino said in KVM vs XenServer:

    I think that the only thing I truly miss in KVM is not a fancy GUI, but instead a stateless host OS 'a la XenServer/ESXi' that I can safely deploy to a usb drive. Something like CentOS atomic host should be good, but focused on KVM instead of Docker.

    You should be able to do a USB install and ship the logs off to somewhere else. Then just mount your disks/volume for the guests.

    I've been thinking of trying that but been too busy/lazy.

    Yes, just mount /var/log elsewhere should do the trick. But it will still lack the "statelessness" of a proper designed hypervisor-centric OS.
    Fedora 26 seems like a good fit…



  • @stacksofplates said in KVM vs XenServer:

    @Francesco-Provino said in KVM vs XenServer:

    I think that the only thing I truly miss in KVM is not a fancy GUI, but instead a stateless host OS 'a la XenServer/ESXi' that I can safely deploy to a usb drive. Something like CentOS atomic host should be good, but focused on KVM instead of Docker.

    You should be able to do a USB install and ship the logs off to somewhere else. Then just mount your disks/volume for the guests.

    I've been thinking of trying that but been too busy/lazy.

    Not having a swap partition or swapfile on the USB too.



  • @black3dynamite said in KVM vs XenServer:

    @stacksofplates said in KVM vs XenServer:

    @Francesco-Provino said in KVM vs XenServer:

    I think that the only thing I truly miss in KVM is not a fancy GUI, but instead a stateless host OS 'a la XenServer/ESXi' that I can safely deploy to a usb drive. Something like CentOS atomic host should be good, but focused on KVM instead of Docker.

    You should be able to do a USB install and ship the logs off to somewhere else. Then just mount your disks/volume for the guests.

    I've been thinking of trying that but been too busy/lazy.

    Not having a swap partition or swapfile on the USB too.

    Ya didn't think of that. I wish there was an easy way to PXE boot RHEL/CentOS to a RAM disk.


  • Service Provider

    @stacksofplates said in KVM vs XenServer:

    I wish there was an easy way to PXE boot RHEL/CentOS to a RAM disk.

    Someone needs to make a small M.2 device with straight DDR4 on it. That would be sweet.


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