[Xen-users] Re: Xen, LVM, DRBD, Linux-HA

["Tomasz Nowak" <tnowak-p@xxxxxxxxxxxxx>]

Rainer Sokoll <rainer@xxxxxxxxxx> wrote:
> I want to put it all together.
> So far, I have a running machine with multiple domUs, and I am very
> excited. But now I want to go a step ahead:
> I have two identical machines with a big amount of RAM and disk space.
> My goal is to hve all the domUs almost redundant - and want to ask you
> for your advice.
> The plan is to have every VM in its own logical volume and have DRBD
> replicate this volume to the other machine. Assumed Linux with
> Linux-HA runs in a VM, here comes my question:
> If the complete Linux VM runs in its own logical volume, Linux-HA
> cannot work, since the configuration must not be the same on both
> sides. One solution would be to have a minor file based backend that
> holds /etc/, /proc/, /var/, /boot/ (and maybe more?). Or maybe there
> is a more sophisticated solution?
> How would you start?
I've developing quite the same solution :)
Machine A will have two separate disks - one for 'local' domUs, second
for machine B domUs replicas). Machine B will also have two disk
drives - one for local domUs and second as A domUs secondary device.

Right now I'm probably in the same place you are (I'm also very
excited :]) but I hope all this is possible due to the fact,
that block device names are exported to domU as virtual names.

So if Dom1a uses /dev/vg0/dom1vda as 'xvda' on machine A,
there is no problem that the same Dom1a would use
/dev/vg1/dom1vda as 'xvda' on machine B. That's just
a difference of /etc/xen/dom1a.cfg on dom0 @A and dom0 @ B,
which probaby should be sligtly different anyway (percheps
less vcpsu and less memeory). Some script that notices
crased Dom1a @ boxA could not only re-create Dom1A @ boxB,
but also execute some other commads like:
xm vcpu-set Dom1b ... and xm mem-set Dom1b ...
to temporarly lower regular recource usage of Dom1b @ boxB.

The only issue I worry about right now is a disk performance,
i.e. how much do I drop of my current ~100MB/s decent speed
(ext3 on LVM2 on S/W Raid10,f2 on 2xSAS SFF 10K)
putting somewhere into all that one more layer - DRDB.

--
Tomek


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