Re: [Xen-users] XEN and clustering?

[Jakov Sosic <jakov.sosic@xxxxxxx>]

On 02/27/2010 02:07 PM, Pasi Kärkkäinen wrote:
> On Sat, Feb 27, 2010 at 11:07:41AM +0100, Jakov Sosic wrote:
>> Hi.
>>
>> I'm using Xen on RHEL cluster, and I have strange problems. I gave raw
>> volumes from storage to Xen virtual machines. With windows, I have a
>> problem that nodes don't see the volume as same one.... for example:
>>
>> clusternode1# clusvcadm -d vm:winxp
>> clusternode1# dd if=/dev/mapper/winxp of=/node1winxp
>> clusternode2# dd if=/dev/mapper/winxp of=/node2winxp
>> clusternode3# dd if=/dev/mapper/winxp of=/node3winxp
>>
>> When I download these files and diff them, they all three differ.
>>
>> Also, sometimes very strange things happen. For example I download some
>> file into winxp, shut it down, then start it on another node, and file
>> is missing?!?!?!?!
>>
>> Should I use maybe CLVM and not raw volumes from storage? Why is this
>> happening?
>>
>
> What kind of xen disk backend are you using? phy:?
> What kind of storage are you using?
>
> When sharing block devices in a cluster across nodes you need
> to make absolutely sure there's no caching going on in dom0s,
> so that the disk contents are always in-sync.
>
> CLVM only helps with safely managing the LVM metadata,
> not with the actual usage of the volumes.

As far as I've managed to test, CLVM actually does resolve this issue. I
don't know how, but starting xen domU on one node, and stopping it, and
after that doing dd of the volume on three nodes gives me exactly the
same binary images without dropping caches. With purely raw volume, I
was not able to achieve this results.


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|    Jakov Sosic    |    ICQ: 28410271    |   PGP: 0x965CAE2D   |
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