From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: Fwd: Corrupted filesystem, possible after livemigration with
 iSCSI storagebackend.
Date: Mon, 15 Mar 2010 08:59:10 -0500
Message-ID: <4B9E3D2E.5090108@codemonkey.ws>
References: <4B9E3A37.5000209@monsternett.no>
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Cc: kvm@vger.kernel.org
To: Espen Berg <espen@monsternett.no>
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On 03/15/2010 08:46 AM, Espen Berg wrote:
> In our KVM system we have two iSCSI backends (master/slave
> configuration) with failover and two KVM hosts supporting live migration.
>
> The iSCSI volumes are shared by the host as a block device in KVM, and
> the volumes are available on both frontends.  After a reboot one of the
> KVMs where not able to start again due to file system corruption.  We
> use XFS and have problems to understand what caused the corruption.
>
> We have ruled out the iSCSI backend as both the master and slave data
> where consistent at the time.
>
> Anyone else had similar problems?  What is the recommended way to share
> an iSCSI drive among the two host machines?
>
> Should XFS be ok as a file system for live migration?  I'm not able to
> find any documentation stating that a clustered file system (GFS2 etc.)
> is recommended.  Are there any concurrent writes on the two host
> machines during a livemigtation?
>
> <disk type='block' device='disk'>
> <driver name='qemu'/>
> <source dev='/dev/disk/by-path/ip-<ip>:3260-iscsi-test2-lun-0'/>
> <target dev='sda' bus='scsi'/>
> <address type='drive' controller='0' bus='0' unit='0'/>
> </disk>

You need to use cache=off if you've got one iscsi drive mounted on two 
separate physical machines.

The additional layer of caching will result in inconsistency because 
iSCSI doesn't have a mechanism to provide cache coherence between two nodes.

Regards,

Anthony Liguori

> #virsh version
> Compiled against library: libvir 0.7.6
> Using library: libvir 0.7.6
> Using API: QEMU 0.7.6
> Running hypervisor: QEMU 0.11.0
>
> #uname -a
> Linux vm01 2.6.32-bpo.2-amd64 #1 SMP Fri Feb 12 16:50:27 UTC 2010 x86_64
> GNU/Linux
>
> Regards
> Espen
>
>
>
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