Re: [Xen-users] Re: Accessing an LV domU

[Alain BARTHE <alain.barthe@xxxxxxxx>]

Hi Simone,

kpartx is our friend :

        kpartx
-a /dev/XenVG/qanew

Then look in /dev/mapper, you should
see a new entry named something like "qanewpa", then

        mount
/dev/mapper/qanewpa /opt/test

should work. If so, do the same with
your swap.

Cheers.

Alain

xen-users-bounces@xxxxxxxxxxxxxxxxxxx a écrit sur
31/03/2008 17:02:42 :

> Hi again,
> 
> I am afraid I will have to ask fro more advice. I have followed the
> suggestions, basically:
> 
> Created an LV /dev/XenVG/qanew and /dev/XenVG/qanew_swap (no 
> filesystem created on it)
> 
> in the conf file for the VM I have:
> 
> disk = [ 'phy:XenVG/qanew,xvda,w', 'phy:XenVG/qanew_swap,xvdb,w' ]
> 
> I create only one partition xvda1 mounted as / and filesystem ext3
> while xvdb1 is used as swap, and GRUB is installed on MBR
> 
> Once the installation is done and the VM is not on, I try to mount
> /dev/XenVG/qanew on /opt/test but it complains I need to specify 
> filesystem, if I run mount -t ext3 .... it complains it is not an
> ext3 filesystem.
> 
> I have been on the net trying to understand where i am going wrong
> but can't seem to find any valid solution. 
> 
> Any further help would be much appreciated.
> 
> Thanks,
> 
> Simone
> 

> On Mon, Mar 31, 2008 at 11:19 AM, Simone <dezmodue@xxxxxxxxx>
wrote:
> Thanks all for your replies. 
> 
> Considering the trouble I would have to go through and the fact that
> I don't need snapshotting within the VM, I am moving to a simpler
> configuration as suggested.
> 
> Thanks again,
> 
> Simone
> 

> On Mon, Mar 31, 2008 at 2:49 AM, Jayson Charles
Vantuyl <
> jvantuyl@xxxxxxxxxxxxxx> wrote:
> It's not so unusual.  It just wasn't easy
to come across before 
> widespread virtualization.
> 
> Nesting LVM setups like this CAN be done, but generally shouldn't.
> 
> Essentially, LVM works by detecting the physical volumes that are
> part of the LVM.  Since you are setting up an LVM that is 
> effectively on another LVM device, the detection can get weird--
> especially if you name an inner LVM volume group the same name as
an
> external LVM volume group.  Let's just say that mixing LVM data
from
> the inner and outer devices can happen, and then things can get really
broken.
> 
> The easiest way to do this (and it's not so easy) is to set up LVM
> to scan your other LVM devices using a second lvm.conf.  Essentially
> you configure both copies of LVM (the internal one and the external
> one) in separate files with careful limits on which devices may be
> scanned for PVs.
> 
> A generally better solution is just to use LVM on the outside and
> pass through the LVs to look like local disks.  The downside
is that
> it requires cooperation from the Dom0 to resize and snapshot; and
> that FS extensions currently require rebooting the VM to pick up the
> size changes.  The upside is the LVM is really simple to manage
if 
> you just do it outside, and the volume is available to the Dom0 for
> mounting like you described.
> 
> Unless you absolutely need snapshotting normally inside or live 
> resizing, I wouldn't go through the trouble of running LVM inside
of
> LVM.  It is fraught with peril.
> 
> I am aware that you are going to have to reinstall your systems, 
> but, if they are doing anything important, you should avoid things
> that can fatally confuse LVM (like nested LVM setups).  While
you're
> at it, don't partition the disks inside of the DomUs either.  Just
> pass through the partitions directly.
> 
> Good luck.
> 
> On Mar 30, 2008, at 4:34 PM, Simone wrote:
> I guess I am trying to do something unusual :)
> 
> Any thoughts?
> 
> Simone
> 

> On Fri, Mar 28, 2008 at 6:47 PM, Simone <dezmodue@xxxxxxxxx>
wrote:
> Hi list,
> 
> I am experiencing with xen on centos5 and so far everything is going
> well, I am really pleased. The domU have a dedicated LV 
> (/dev/vg1/xenVM1, /dev/vg1/xenVM2 etc) and the guest OS is Centos4.
> At guest install time I have choosen to use LVM so that also inside
> the guest I have /dev/vg0/root, /dev/vg0/tmp etc. Is there a way to
> mount and edit the guest filesystem to customize files etc?
> The idea would be to have a guest template that can be cloned and
> then edited to generate new VMs.
> 
> Thanks, have a good weekend
> 
> Simone
> 

> 
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> 
> 

> -- 
> Jayson Vantuyl
> Systems Architect
> Engine Yard
> jvantuyl@xxxxxxxxxxxxxx
> 1 866 518 9275 ext 204
> 
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