Re: [Xen-users] vbd Sharing

[Tim Post <tim.post@xxxxxxxxxxxxxxx>]

On Tue, 2007-02-06 at 02:53 +0100, Florian Heigl wrote:
> Hi,
> 
> I'm currently working on some clustering howto and trying to do my
> work with an increasing number of Xen domUs. They run fedora core 6
> and are intended to share a number of OCFS2 filesystems, which all
> reside on an EVMS volume.
> 
> I'm now looking for a _clean_ way of enabling shared rw access.

The only time this is an issue is when more than 1 guest using the
cluster FS is on the same physical dom-0 node. 

the "w!" flag when specifying the VBD works very well. If your dom-u's
root file system is ocfs2, be sure to specify an appropriate initrd to
do the following :

bring up eth(x) and (if iscsi) configure it.
some means of obtaining a centralized cluster.conf if so desired
modprobe ocfs2

.. pivot_root 

Then o2cb will take over the rest. I really recommend booting to a small
local vbd, then arrange fstab in such a way that you facilitate your
single system image if so desired.

>  I know
> people have already done this, the only documented way I found so far
> included hacking /etc/xen/scripts/block to the grade of disabling the
> whole check it's intended to do, which isn't 'production grade' :)

You did a sort of difficult search. Quite a bit of what turns up in the
top 10 via any reasonable keyword search phrase will give you out dated
information.

> 
> I agree blocking shared rw accesses in general is a good thing [tm],
> but I wonder what to do about the cases where it's not.

This was "polished" quite a bit.

> I could of course map the volumes to my fileserver and generate an
> iSCSI target there, but I think I have other ways of maximizing
> overhead :)

AoE is *very* nice for this, and has a very small overhead cost, and no
need for tcp offload cards since its a routless protocol. I recommend
looking into it, migrating becomes very easy once you do.

> 
> Any takers?
> If not, who do should I submit a patch for 'block' to?
> 
> Regards,
> Florian

Hope this helps.

Best,
--Tim


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