Re: [Xen-users] Xen on two node DRBD cluster with Pacemaker

[Bart Coninckx <bart.coninckx@xxxxxxxxxx>]

On Thursday 20 January 2011 09:44:47 Jean Baptiste Favre wrote:
> Hello Bart,
> Answers inline.
> 
> Le 19/01/2011 21:49, Bart Coninckx a écrit :
> > On Wednesday 19 January 2011 21:15:46 Jean Baptiste FAVRE wrote:
> >> Hello Bart,
> >> I wrote such an howto some times ago. It's available here in french
> >> (http://publications.jbfavre.org/virtualisation/cluster-xen-corosync-pac
> >> ema ker-drbd-ocfs2.fr) and here in english
> >> (http://publications.jbfavre.org/virtualisation/cluster-xen-corosync-pac
> >> ema ker-drbd-ocfs2.en).
> >> 
> >> It's LVM based but could be easily adapted for img files.
> >> 
> >> Regards,
> >> JB
> >> 
> >> Le 19/01/2011 17:54, Bart Coninckx a écrit :
> >>> Hi all,
> >>> 
> >>> could somebody point me to what is considered a sound way to offer Xen
> >>> guests on a two node DRBD cluster in combination with Pacemaker? I
> >>> prefer block devices over images for the DomU's. I understand that for
> >>> live migration DRBD 8.3 is needed, but I'm not sure as to what kind of
> >>> resource
> >>> agents/technologies are advised (LVM,cLVM, ...) and what kind of DRBD
> >>> config (seperate devices for each DomU I guess?)
> >>> Thank you!
> >>> Bart
> > 
> > Hi Jean,
> > 
> > thank you for this document, it seems highly educational. Could you
> > please verify if I understand correctly:
> > 
> > - you use LVM to build your DRBD resources on (not the other way around)
> 
> At dom0 level, I have 2 VG:
> - system, for... system :)
> - XenHosting, for domUs and common Xen related FS
> 
> Inside XenHosting, I create LVs:
> - One for common stuff (config, kernels, iso, ...).
> - One for each domU
> 
> Each LV are defined as DRBD resources.
> 
> Having one DRBD ressource per domU allow you to migrate them
> independently. More, if your cluster grows and get a third server, you
> can balance DRBD ressources between them. It's just easier to manage.
> 
> Each domU boots on its LV. That means that at domU level, your DRBD
> ressource (or LV) is saw as a disk. Then you install your domU system.
> The way I install domUs makes me use LV as well
> 
> As a summary, you have LV inside DRBD ressource onto LV.
> It seems complicated but in fact it's not so tricky :)
> 
> If you want to use img files, either you store them on one LV only, and
> you'll have to create cluster FS on it, or you use separate LV. In case
> of separate LV, I prefer installing domU in LV directly instead of using
> img file because it's easier to access LV based FS from dom0 in case
> domU crashes.
> 
> > - you use a DRBD resource with a OCFS2 filesystem on to offer the ISO's
> > and config files on both nodes for every DomU
> 
> Yes, using cluster FS allow you to mount it on each node and provides
> concurrent access for each dom0. I choose OCFS2 at the time of writing,
> but I had to do it now, I would give a try to GlusterFS.
> 
> You can choose another way (like rsync), but I prefer cluster FS as I
> don't have to think about synchronisation.
> 
> > - for each DomU you create a seperate DRBD resource that is allowed to be
> > dual primary so you can do live migrations.
> 
> You MUST allow dual primary if you want to use live migration. So it's
> not cluster specific.
> 
> > Am I doing all right?  ;-)
> 
> Yep, seems ;)
> 
> Regards,
> JB
> 
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Jean,

all clear, except for the LVM on top of the DRBD resource: is that LV created 
on Dom0 or during the installation of Dom0.

It seems a sound way of implementing stuff. I roughly did the same in the past 
but with an external Pacemaker for an iSCSI cluster. Since this project is 
without it, I was a bit unsure a to how doing the live migration and such. 

You don't use any stonith?


B.




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