Re: [Xen-users] migrating with physical device as VBD

[Jan Schulze <schulze@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Ross S. W. Walker wrote:
> Jan Schulze wrote:
>> Hi all,
>>
>> I am wondering, whether it's possible to migrate a DomU from one XEN Host to
>> another *without* using shared storage. All HowTos that I found so far, are
>> using some kind of shared filesystem or block device.
> 
> Shared storage is mandatory, but it doesn't have to be traditional multi-host
> scsi or fiber channel, with technology like iscsi and software like drbd
> shared storage can be done on the cheap.
> 
>> The DomU in question is using a physical device (partition /dev/sda1) that is
>> exported as VBD from Dom0. If migration is possible with that setup, where 
>> will
>> the DomU end up on the target system?
> 
> It needs to be accessible there too at the same time, thus why shared storage
> is mandatory. Check out drbd, the latest version does primary-primary which
> is what you need for live migrations.

DRBD seems really interesting. However, when using primary-primary, I
would also need a cluster file system. As my existing DomU uses ext3, I
won't be able to use DRBD in a primary-primary setup, right?


>> In case, migrating this DomU won't work, I would have to copy the VM 
>> manually.
>> Is it possible to access the contents of /dev/sda1 from Dom0? Simply shutting
>> down the DomU and mounting /dev/sda1 in Dom0 does not work.
> 
> There will be a partition table within that partition, so you can run
> kpartx -a /dev/sda1, and access the first partition via /dev/mapper/sda11,
> or mount it via a loopback mount to the offset of that partition.
> 
> # mount -t <fstype> -oloop,offset=<part offset> /dev/sda1 /mnt

Thanks, did not know that. Very useful.


Regards,
Jan

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