Hi,

I am trying to decide which OS to use to set up a server for virtual machines. I have been given a Dell R620 server to play with and I like to set this up with different flavors of Linux using virtual machines.

I am having a hard time to make the distinction between the free open source version and the non free versions, as there seems to be a big overlap between the two. My server driver package has support for; Red Hat, Suse and Xen. So I like to start with these to make live easy

I believe RedHat isn't for free, but I think Xen and Suse do have a free version, but there is where my confusion kicks in.

I think that Xen-project is the open source free version but Citrix XenServer isn't, although they have a free Xenserver7.6, but that is no longer supported as it is past its expiration date. I have checked on my hardware end and at the software end if my server hardware is supported, and Xen 6,7,8 seems to be supported on both ends.

I am under the impression that Xen-project is geared towards light weight hardware and is based around the x86 architecture, which probably makes it not very useful for a server.

Suse seems to only offer a free trial version with 60 days support. That is leaving me with openSUSE Leap I believe, as my host OS which seems to support the Xen and KVM Hypervisor.

Am I on the right track, or have I missed something?

I find it confusing as in the end everything seems to be linked to, or overlap each other, and at the same time go their own way into a free or non free direction. I am not sure, but I think it is important to find software that my hardware is supporting, but feel free to convince me otherwise.

Yes, RHEL is not free.
The free version of Red Hat Enterprise Linux (RHEL) is CentOS. I don't know about the other flavors.

I have just been reading up on this. CentOS does support KVM but doesn't support Xen?

Do you know if there is a difference between using KVM and Xen?

Sorry, I don't know anything about either of those packages.

Yes
There is. In a nutshell (I don't know that much about Xen; for details, use the internet):

KVM

KVM is known as a type 2 hypervisor. Virtual machines run as processes on a regular operating system installation.

KVM workflow

You install Centos or another OS, install the KVM software on it, then create virtual machines from the Bash command line or using the GUI virtual machine manager.

Xen

Xen is a type 1 hypervisor. This means that the hypervisor does not run on a regular operating system installation, but it is the operating system.

Xen workflow

You install Xen onto the bare-metal server, start up virtual machine number 0, and start additional virtual machines from machine 1.

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Like RHEL, SUSE has a paid-for version with enterprise-level support named SUSE Linux Enterprise server (SLES), and a totally free (as in beer and freedom) community-supported version named OpenSUSE. I am not sure though if there are differences between OpenSUSE and SLES. Differences between Centos and RHEL are practically zero.
You have to understand that Red Hat and SUSE are companies that must make a profit or go out of business. To make it clear to the open-source community and to their customers, they give their paid-for product a different name than their community-supported version. Canonical, the third big vendor, chooses to have a single version named Ubuntu.

Of course everything overlaps each other, because everything is based on Linux, GNU and other software.
You are right, but your server is Dell, which is so mainstream it almost hurts. If it is not extremely old, you can be fairly certain that all mainstream Linux distros will run well on it.

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Well I do a search first which often lead to many more questions.(As I am new to Linux there is a bit of an information overload to work through that could be reduced with some help by asking questions) But in general terms XEN and KVM seem very similar on the surface.
XEN seems to have better driver support for VM's running Windows, while KVM seems to work better with VM's running Linux.
If Xen is used via OpenSuse it no longer is a type 1 Hypervisor I believe? And is there an installation ISO of XEN as a type 1? I am under the impression that you have to create/compile one yourself.

The other thing that has me wonder, is that when I search for XEN in thread titles on this forum it comes back with 17 pages of search results, but the first page of search results has a time span of 4+ years. Is XEN not very popular and have people started to move away from it?

Both can be driven with libvirt (which was originally written as a better interface to Xen). I would guess that by far most users use libvirt as the interface to either KVM or Xen.

I believe driver support is quite irrelevant. Drivers for your hardware are provided by the operating system, OpenSUSE, Centos or whatever else it might be, not by KVM. KVM's guests most likely don't use hardware drivers, but virtio drivers for storage and networking.

Most probably Xen is much less popular than KVM, although it was the first open-source hypervisor as far as I know. My guess is that it's much easier to install KVM, being type 2, than Xen.

Regarding type 1 or 2, and OpenSUSE with Xen, see this PDF document: https://doc.opensuse.org/documentati...t_color_en.pdf, in particular the diagram on page 9, which shows that Xen runs directly on the bare metal.

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Unless that server has some kind of super custom stuff any distro should run it just fine. Debian, Ubuntu as well as the ones you listed. I'm personally partial to Debian. I've heard it said Debian is so stable it hardly breathes. Of what you listed CentOS is the only real choice. Suse doesn't seem very popular and as such support will be limited compared to CentOS or the Debian ecosystems. I've played with Xen a bit, KVM wins for me every single time. Ubuntu will give you easy access to LXD containers as well, those are tough to beat. Use them extensively in my home. Near full vm experience while getting bare metal peformance.

If it was for my personal use in my home, I'd run Ubuntu LTS on it. Actual workloads where things matter? Debian without question.

Thank you for the document, that is going to be handy.

Out of curiosity, is the initial OpenSuse install converted to a Dom0 virtual machine, or is it something like a dual boot setup?

Chapter 6.2 in this document shows how you enable Xen from Yast. Yes, you first install the OS, then Xen.

However, you then boot into the Xen kernel instead of the OpenSUSE kernel. I.e., you boot the Xen hypervisor, and then OpenSUSE as domain 0. With KVM, you boot the normal OS kernel, then launch KVM machines as qemu processes running on the OS.

Many thanks.

I have tried CentOS and Xen today, but cannot get XEN to start. I am going to try OpenSUSE next.
When installing OpenSUSE on a new disk, do I let OpenSUSE partition the whole drive, or am I going to create a small partition to install OpenSUSE, and let XEN partition the rest of the drive?

I have never used Xen; I don't know. It looks like Xen uses the root filesystem, and there is no need for a particular storage configuration.