Topic: Virtualization - Vmware versus Xen.

[arne]

At the present time I have two virtual servers runing:

1. A SME 7.3 gateway with Vmware and a aditional sme 7.3 vitual server pluss a virtual Windows client for remote access, etc.

2. A Centos 5.1/64 running with Xen and a virtual SME 7.3 installation.

I have tried to test a bit to see what is the best or optimum virtualization system, and these are my conlusions just now. (That might be considered to be completely incorrect after some more learning, discussions and testing etc):

1. When it comes to userfriendliness and flexibility and ease of use the Vmware is the clear winner.

2. Using Vmware server SME 7.3 can be used as a host operation system and as a guest operation system and works and performs rather nice. Using Xen there is only one choice, SME 7.3 can only run as "guest" as it does not contain the modified kernel that is required for a Xen host system.

3. When it comes to power and performance the Xen installation is the clear winner.

4. If you want to run a SME 7.3 as a virtual installation on a 64 bit platform both Vmware and Xen can do that job.

Conclusion:

1. Vmware is the most easy virtualization platform to get started with.

2. If the performance of a Vmware installation is enough and if it works stable enough, there is no reason to change over to Xen.

3. If you want an easy graphical admin console that can be used from a Windows platform, Vmware is the choice.

3. If more performace (power) is needed, then Xen is the choice. (And SME 7.3 on Xen/Centos5.1/64 really "flyes".)


Is there other opinions about this subject ? Am I wrong, is it something I have missed, some other point of views, something more that should be tested or questions or ideas that can lead to a bether learning and understanding of this virtualization technology ?

[cactus]

Is there other opinions about this subject ? Am I wrong, is it something I have missed, some other point of views, something more that should be tested or questions or ideas that can lead to a bether learning and understanding of this virtualization technology ?

The big difference between Xen and VMWare is that Xen allows you direct access to hardware in your machine, for instance modem or TV card, where VMWare does not allow you access hardware directly. You have to have a VMWare driver emulating the device for you in VMWare.

[william_syd]

2. Using Vmware server SME 7.3 can be used as a host operation system and as a guest operation system and works and performs rather nice. Using Xen there is only one choice, SME 7.3 can only run as "guest" as it does not contain the modified kernel that is required for a Xen host system.

1. Can the Xen kernel from centosplus be used?

http://mirrors.kernel.org/centos/4.6/centosplus/i386/RPMS/

2. If so, what other libraries and support files are required, if any?

[cactus]

1. Can the Xen kernel from centosplus be used?

http://mirrors.kernel.org/centos/4.6/centosplus/i386/RPMS/

2. If so, what other libraries and support files are required, if any?

AFAIK you do not need to, if you have a look on the installation CD's you should find a kernel-xenU as well, this is the smeserver guest XEN kernel.

[william_syd]

AFAIK you do not need to, if you have a look on the installation CD's you should find a kernel-xenU as well, this is the smeserver guest XEN kernel.

I'm not familiar with Xen at all.

Which needs the special kernel, the host or the guest?

[arne]

There is a number of ways of doing this thing and there is also a big secret about using Xen on Centos 5.1/32/64.

The big secret is:

The text based xenconsole of Centos 5.1 is more than buggy, it does not work at all (at least not when installed using rpm's)

On the other hand RedHat has made a quite good job when they made the intergration of the graphical xenconsole into the Gnome enviroment. So you will just have to install Gnome and it will all work "plug and play" just after a "click". (I used a week on it to realize that it all could could actually all be done in 5 minutes.)

Actually it is difficult like this http://www.cyberciti.biz/tips/rhel-centos-xen-virtualization-installation-howto.html , while the text based approach will lead you into cicles and circles and to discussion boards with no answers.

There is basically two ways of doing the Virtualization under Xen, "paravitualization" or something like that where the "guest" comunicates more or less direct with the hardware and "full virtualization" where it more works like Vmware.

The Xen host will allways require a customized xen enabled kernel.

The "guest" system will require a customized kernel if you want to do a "paravirtualized" installation (with direct hardware access) but if you do a installation based on "full virtualization" you will only need the standard kernel.

When you are doing these things under Centos51/64/Gnome allmost everything is automated and you will just have to insert the SME 7.3 standard CDROM and it is all more plug and play. (But the plug and play of Vmware is the best one.)

[imcintyre]

I gather that you are using a 64 bit processor and AFAIK, xen requires 64 bit processor? Would you please detail what you know re this so that the more budget minded of us don't get off on the wrong track.

[arne]

OK, I had to google and find out what this new technical deign AFAIK is, and now I know

As I had red from the Centos documentation I think I have read that it will require a 64 bit processor and that an 32 bit kernel can not run on a Xen 64 bit Xen/Centos installation, but the last statement is at least wrong. The Centos 5.1/32 does contain xen, and should it then be a requirement to run Centos 32 on a 64 bit processor ? It does not sound reasonable, does it ?

I will see if I can get it tested on an old Atlon 900 if I can get this one up and running. My guess is that the Xen will work on Centos 5.1/32 even though I think I have red the oposite  ... (??)

****

Doing a netbased Centos 5.1/32 installation on the old Athlon just now. Will let you know during the day if it will run with Xen or not.

[arne]

Anybody who have tried:

A. To run Windows 2000/XP under Xen ?

B. To connect a USB unit like a Web cam to a Virtual Machine under Zen ?

???

(Acording to the theory Xen should have the best hardware support. Theory and reality does not on the other hand allways agree.)
(But it would be interesing if ir were possible to run virtual Windows installations using USB units.)

[tec]

Hi,
maybe I can fill some questions here out.

As Arne stated Xen uses 2 differente modes for virtual machines. For Paravirtualized you need a special Xen-Guest-Kernel. For HVM you need a processor that uses Pacifica or Vanderpool but you can use the normal kernel.

I think it was with introduced with Xen 3.1 that you can run 32bit Guest on a 64Bit Host system. But I have no knowledge how to do this.
Xen does not requiere 64Bit Hosts. I have it running on a 32Bit Debianbased host.

The biggest advantage of Xen is the feature of passing PCI devices to the guest. But for this feature you need at least a Xen-Guest Kernel with 2.6.18.  The current 2.6.9 SME Kernel does not support the usage of "pcibackhided" devices.

Yes you can run Windows2000/XP under Xen IF you have an Ahtlon X2 or Intel Core2Duo e.g. a processor that useses hardware virtualization. But it runs really slow and the installation goes ages. Maybe if you are using Enterprise Version from Novel or Xen you get special drivers for Windows under Xen, similiar to the VMware-Tools
You can use USB devices in a guest BUT it only works in paravirtualized mode and for this you need to pass the USB Bus to the virtual machine.

If there are further question, please ask

[arne]

I think it was with introduced with Xen 3.1 that you can run 32bit Guest on a 64Bit Host system. But I have no knowledge how to do this.

This just worked out of the box with the Gnome/Centos variant of installation. (Even though the Centos manual says it shouldn't. Guess it is not updated from 5.0)

***
Looks like the old Atlon 900 is running with Xen. Will just do some updates and try to install SME 7.3 ..

[slords]

The big secret is:

The text based xenconsole of Centos 5.1 is more than buggy, it does not work at all (at least not when installed using rpm's)

On the other hand RedHat has made a quite good job when they made the intergration of the graphical xenconsole into the Gnome enviroment. So you will just have to install Gnome and it will all work "plug and play" just after a "click". (I used a week on it to realize that it all could could actually all be done in 5 minutes.)

Actually it is difficult like this http://www.cyberciti.biz/tips/rhel-centos-xen-virtualization-installation-howto.html , while the text based approach will lead you into cicles and circles and to discussion boards with no answers.

Not true.  I'm running the text based console for all my xen hosts and haven't ever had an issue.

The Xen host will allways require a customized xen enabled kernel.

The "guest" system will require a customized kernel if you want to do a "paravirtualized" installation (with direct hardware access) but if you do a installation based on "full virtualization" you will only need the standard kernel.

I think you are a little mixed up.  You don't need any customized kernel at all.  You need a xen kernel that is provided by RHEL/CentOS/SME.  It is no different then needing to install the smp kernel for a multi-processor box.

[tec]

Sorry ,
that i didnt use the right terminology. I meant with customized-kernel = Xen-Kernel.

[arne]

slords ->

Not true.  I'm running the text based console for all my xen hosts and haven't ever had an issue.

Yes, but I repeated the problem again and again at least at 10 following installations and each time I ended up with a text based console that was hanging. When searching on Google, on the error messages that apeared, I could find, I think houdreds of descriptions of the same problem, with no solution.

Could it be that this problem is related to one certain installation method or some certain hardware ? (I actually still have a hardware related bug, and that is Xen can not see all memory, only 3.2 GB but I know it is a AMD64/BIOS/Controller problem.)

1. Did you use the RPM or the kernel source for installation ?

2. Do you use a AMD64 or an Intel processor ? 

The same problem ? http://bugs.contribs.org/show_bug.cgi?id=3663


imcintyre ->

It apeared that the old Athlon came up with the option of paravirtualized but not full installation and then net based installation as the only option. I first tried with a sme os site, but this dis not work (  http://smemirror.fullnet.co.uk/releases/7.3/smeos/i386/ ) Next try was the Centos mirror in Sweeden. I am now doing a paravirtualized installation of Centos 5.1 on this machine to see how this will work.

***

While the Vmware platform seems to be working more or less equally from hardware to hardware, there seems to be variations of how the Xen platform will work.

[slords]

Could it be that this problem is related to one certain installation method or some certain hardware ? (I actually still have a hardware related bug, and that is Xen can not see all memory, only 3.2 GB but I know it is a AMD64/BIOS/Controller problem.)

No memory issues here.  I run 4 different dom0 machines all running stripped down CentOS 5.1/32.  All have 12GB of memory and they all see the full amount.

1. Did you use the RPM or the kernel source for installation ?

Everything is stock CentOS rpms.  I didn't install anything extra from anywhere else except for the standard rpms.  I have a total of 215 rpms installed and that is it.

2. Do you use a AMD64 or an Intel processor ?

My boxes are all Server class Intel Xeon machines.  I do have one small AMD box that I use to compile the 64-bit packages on that is also running xen0 and I haven't experienced any issue on that one either.

The same problem ? http://bugs.contribs.org/show_bug.cgi?id=3663

That bug deals with the server-console (sme8 specific) being messed up after the install has completed.  If you install anything other then sme8 then the console has no issues.

It apeared that the old Athlon came up with the option of paravirtualized but not full installation and then net based installation as the only option. I first tried with a sme os site, but this dis not work (  http://smemirror.fullnet.co.uk/releases/7.3/smeos/i386/ ) Next try was the Centos mirror in Sweeden. I am now doing a paravirtualized installation of Centos 5.1 on this machine to see how this will work.

All of my installations are paravirtualized installs.  I'm not sure what your issue is but I can install directly from ibiblio (or my local master mirror) without any issues at all.  I just issue the commands I posted elsewhere in the forums and in about 4 minutes I have a fulling running paravirtualized install of sme running in either server-only or server-and-gateway mode.  The only issues I've seen (other then the console with sme8) is that there are a few issues with iptables rules we have setup and how things are tagged by the bridge on dom0.