RE: [Xen-users] Domain-0 freezes when mounting a cloned domU with dd

["Artur Linhart - Linux communication" <AL.LINUX@xxxxxxxxxxx>]

Hello,

        Because I use LVM for creation of logical volumes for DomU, I make
the backup so I shutdown the DomU, then create a snapshot volume and then
start again the DomU... Then I can dd the snapshotted volume with the
consistent state...

        At least I hope this is the safe and clear way how to do it, because
the LVM subsystem has to handle itself such a problematic situations you
write about and should "somehow" perform the flush of all caches before the
snapshot is created, or - even if it would not be written everything to the
disk - LVM should make it transparent to You also without having all data
really written to the "iron" device... At least I do not know abot nobody
who would say something different :-)...

        If You do not use LVM, I do not know how to flush the caches, but
I'm sure somewhere must be someutility which is able to do it... Maybe (?)
at least if You try to mount the device from Dom0 after DomU has been shut
down I think this could help - I canot imagine the volume could be mounted
in the inconsistent state - but it is only my feeling and I am no Linux guru
:-)

        With regards

                Archie

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Franck ELIE
Sent: Monday, August 20, 2007 5:25 PM
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Domain-0 freezes when mounting a cloned domU with
dd

Franck ELIE a écrit :
> Hi
>
> When cloning à domU with 'dd' command (after a domU shutdown), it 
> seems to be very important to perform a 'fsck' on cloned partitions 
> before to mount because if we don't, it freezes Domain-0 and next dom-U.
>
> Just before the kernel froze, logs are full of such message :
> kernel: 
>
>>ext3_orp>ext3_orph>ext3_orph>ext3_orph>ext3_orpha>ext3_orp>ext3_orpha>ext3
_or>ext3_or>ext3_orph>e 
>
>
xt3_orp>ext3_orp>ext3_orph>ext3_or>ext3_orpha>ext3_or>ext3_orp>ext3_or>ext3_
orp>ext3_orph>ext3_orpha>ext3_or>ext3_orp>ext3_orp>ext3_ 
>
or>ext3_orphan>ext3_orphan_>ext3_orpha>ext3_orp>ext3_orp>ext3_orph>ext3_orph
an>ext3_orp>ext3_orp>ext3_orph> 
> ....
>
> Note that when performing a fdisk on such partitions I obtain this 
> output :
> # fsck.ext3 /dev/mapper/CMS1
> e2fsck 1.40-WIP (14-Nov-2006)
> /dev/mapper/CMS1: recovering journal
> Truncating orphaned inode 32474 (uid=101, gid=104, mode=0140777, size=0)
> /dev/mapper/CMS1: clean, 37928/221312 files, 250275/441779 blocks
>
> By the way, fsck on the template domU seems to be OK.
>
> So, here are my questions :
> - Do you know why is it necessary to perform fsck ? Should I use 
> specific options with dd to avoid this effect on the cloned FS ?
> - Concerning the kernel freeze (that seems not to be specific to my 
> distrib or xen),  is it a kernel bug ?
>
> Regards
>
>  Franck
>
> P.S.: xen 3.03, kernel 2.6.18-4-xen-686, Debian Etch, 1 domU per LUN 
> of 2Go, no LVM
>

Here are the result of tests I just performed to understand what 's wrong :
- there is a MD5 difference between the sum computed from LUN of the 
domU storage and the image file generated with 'dd' WHEN the backup is 
performed just after the domU shutdown (less than 3min).
- domain-0 have enough memory (8Go) to copy the domU (2Go)

So, my FS trouble would to be related with a partial copy of domU that 
seems to be performed with 'dd' before before the end of the memory 
flush away to disk domU.

So do you know how to perform the memory flush related to a domU in 
order to backup the disk correctly ?

Any suggestion would be appreciate

Regards

  Franck



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