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

[Bart Coninckx <bart.coninckx@xxxxxxxxxx>]

On Thursday 20 January 2011 11:37:58 Bart Coninckx wrote:
> 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-p
> > >> ac ema ker-drbd-ocfs2.fr) and here in english
> > >> (http://publications.jbfavre.org/virtualisation/cluster-xen-corosync-p
> > >> ac 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
> > 
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-users
> 
> 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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Oops, I mean:

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

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