trying to get a domU to manage lvm pvs

trying to get a domU to manage lvm pvs

[Tupshin Harper]

I'm trying to have a domU run lvm and manage one vg, a few pvs, and lots 
of lvs without the dom0 having any role in the situation.

To simplify things as much as possible, I set up a test with one pv, 
that is recognized as such by the dom0, and I'm using the same dom0 
kernel for my domU.

I did the following:
* pvcreate /dev/hda6 from dom0, and verified that pvscan showed it
* I then explicitly excluded it in dom0's lvm filter, and verified that 
pvscan did not see it
* I added an entry ('phy:hda6,hda6,w') to the domU's  disk configuration
* started the domU
* did a "dd if=/dev/hda6 | less" and saw that the device existed and 
contained information indication it was  a pv.
* copied the exact lvm.conf that I was using in dom0 before adding the 
hda6 exclusion
* restarted lvm (and later rebooted the domU just to be certain)
* did a pvscan and pvdisplay /dev/hda6, both of which claimed to not see 
anything
* tried to redo the pvcreate from within the domU and got the message: 
"/dev/hda6: Couldn't find device.  Check your filters?" (triple checked 
the filters)
* noted that /etc/lvm/.cache consistently is getting filled with:
        valid_devices=[
                "/dev/loop0",
                "/dev/loop1",
                "/dev/loop3",
                "/dev/loop4",
                "/dev/loop7",
                "/dev/loop2",
                "/dev/md0",
                "/dev/loop5",
                "/dev/loop6"
        ]
instead of the specific device(s) that I am handing off to the domU. The 
dom0 lvm cache contains none of those entries.

Any suggestions?


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Re: trying to get a domU to manage lvm pvs

[Tupshin Harper]

Tupshin Harper wrote:

> I'm trying to have a domU run lvm and manage one vg, a few pvs, and 
> lots of lvs without the dom0 having any role in the situation.

One more piece of info. If I turn up lvm logging to debug level I see this:

    Using physical volume(s) on command line
        /dev/hda6: Added to device cache
        /dev/hda6: Skipping: Unrecognised LVM device type 3
        /dev/hda6: Skipping (cached)
  Failed to read physical volume "/dev/hda7"


At this point, it seems that xen exports a block device with some 
information different enough than the original block device that it's 
tripping up lvm, but I have no idea what that might be. Has anybody had 
lvm working in a domU?

-Tupshin


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Re: trying to get a domU to manage lvm pvs

[Christian Limpach]

On Fri, 11 Feb 2005 14:48:54 -0800, Tupshin Harper <tupshin@tupshin.com> wrote:
> Tupshin Harper wrote:
> 
> > I'm trying to have a domU run lvm and manage one vg, a few pvs, and
> > lots of lvs without the dom0 having any role in the situation.
> 
> One more piece of info. If I turn up lvm logging to debug level I see this:
> 
>    Using physical volume(s) on command line
>        /dev/hda6: Added to device cache
>        /dev/hda6: Skipping: Unrecognised LVM device type 3
>        /dev/hda6: Skipping (cached)
>  Failed to read physical volume "/dev/hda7"
> 
> At this point, it seems that xen exports a block device with some
> information different enough than the original block device that it's
> tripping up lvm, but I have no idea what that might be. Has anybody had
> lvm working in a domU?

It was actually the import which named ide devices slightly different
than the normal ide driver and lvm has hard coded table of device
names and ignores all other devices.  I've fixed this now in
xen-2.0-testing and xen-unstable.  It should work with the version you
have, if you export your pv's to a sd device in domU (sda7 instead of
hda7).

     christian


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Re: trying to get a domU to manage lvm pvs (SUCCESS)

[Tupshin Harper]

Christian Limpach wrote:

> It was actually the import which named ide devices slightly different
>
>than the normal ide driver and lvm has hard coded table of device
>names and ignores all other devices.  I've fixed this now in
>xen-2.0-testing and xen-unstable.  It should work with the version you
>have, if you export your pv's to a sd device in domU (sda7 instead of
>hda7).
>
>     christian
>  
>
Wonderful. Thank you thank you thank you. :)

I tried the switch to sda and that does indeed work fine (I'll try the 
fix for hda soon). More importantly, it works perfectly with the more 
complex scenario I was attempting which was to export 3 raid5 md devices 
which are the actual pvs for the vg that I want managed by the domU.

My disk setup now looks like this:
disk = [ 'phy:xen_vg/fileserver,hda1,w',
         'phy:xen_swap_vg/fileserver,hda2,w',
         'phy:md2,sda2,w',
         'phy:md3,sda3,w',
         'phy:md4,sda4,w',
       ]

I have my dom0 entirely on md0 (raid1), with its swap on md1(raid1). I 
have a number of xenU's, each occupying a lv on a raid5 backed vg 
(xen_vg above), with each of them having swap space allocated on a 
another raid1 backed vg (xen_swap_vg above), and then 3 raid fives that 
collectively make up the vg that my "fileserver" xenU manages.

Initial testing says that it works flawlessly. Woo hoo.

-Tupshin


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