Xen: Smp & Lvm

Discussion in 'HOWTO-Related Questions' started by zokahn, Jan 23, 2006.

  1. zokahn

    zokahn New Member


    I've tested a Xen setup on Debian 3.1 on a single CPU system. All was well, a few problems but these can be solved ;-)

    However, while i'm doing the setup on a dual Xeon starten me wondering. Is the host kernel SMP capable? I really hope so!

    My second question is more on Xen and LVM. On my test system I just followed the manual and created a single root (ext3) and a swap filesystem. On my definite system i want LVM as I don't really know the future growth behaviour. Now I have /boot as seperate ext3 (for grub) and the rest in a LVM array (/, /var, /tmp etc as JFS) But the Xen kernel won't boot! Has anyone tried a somethin like this? I can always pull / out of lvm and make it a ext3 outside LVM while keeping data filesystems in LVM.

    So two questions: Is the Host kernel SMP capable? and Is the Host kernel LVM capable?

    Kind regards,

  2. falko

    falko Super Moderator Howtoforge Staff

    Did you install Xen from the sources or from the pre-compiled binaries?
  3. zokahn

    zokahn New Member

    i used sources on debian sarge. i would like to able to use lvm all the way.
    looked at xen 3.0 at found that it supports smp for guests. would you choose xen 3.0 or wait for 3.1?

  4. falko

    falko Super Moderator Howtoforge Staff

    You can have a look at the kernel's config file in boot if SMP and LVM are enabled.

    I'm having some problems with Xen 3.0 and virtual networks right now. It doesn't work like described here: http://www.howtoforge.com/perfect_xen_setup_debian_ubuntu_p6, and I'm still waiting for an answer from the Xen mailing list... :( That's why I'd stick with Xen 2.0.7 for now.
  5. zokahn

    zokahn New Member

    Soooooo... You are saying that I can use VLM, even for / once i´ve got my kernel options sorted? I hope so.

    I´ll experiment with some options. Right now i´m installing using a lvm-less setup, only some file systems on lvm (not /boot and not /). Then i´ll finaly see how xen will work on my 2 xeons... Really exited, as i really love having all these enterprise toys put to good open source use :D

    love your work falko, i was reading your stuff even before howtoforge... Excelent!


  6. zokahn

    zokahn New Member

    I´ve now done the setup and it works correctly...

    LVM for /boot is not possible as GRUB has a problem with it. LVM for / is not possible as Xen won´t load the right modules and it does not do the vgchange -a y vgscan thingies... I think it can be done by building a ramdisk (a next project ;) )
    LVM for other filesystems is possible: I now have it running with only my /var and a data volume /local in LVM. This will make snapshot backups, extending filesystems en moving to new hardware easy...

    SMP with Xen is kinda strange. You really get the feelling you are building a single cpu kernel as the XEN config will not show the SMP options in de CPU section. After booting from the succesfull kernel build you will not see additional CPU´s in the top program.

    However XEN will use ALL the processors availible for loading the virtual machines, you can even assign a CPU in the config file by setting cpu=0 or cpu=1 or cpu=#.

    A SMP virtual machine is not possible in XEN 2.0. A virtual machine can only use 1 cpu. All that goodness is saved for XEN 3.0 where that is possible... However, Falko seems to have found a bug in networking with Xen 3, and i guess solving it will take it´s time.

    :D Thanks!


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