[CentOS-virt] xen+drbd Question

Ross S. W. Walker RWalker at medallion.com
Tue Aug 26 14:43:02 UTC 2008

Alexandre Biancalana wrote:
> Hi list,
>  I installed two new servers to be our virtualization HA. This servers
> have CentOS 5.2, Xen 3.0.3, Drbd 8.2.6. The setup is ok, lvm drbd
> resources sincronizing, Guest VM running without any problem.
> My only doubt is that I can only use drbd resources inside guest vms
> when I specify the disk resource in vms config like this:
> disk   = ['phy:/dev/VolGroup00/vappprtem01,hda,w' ]
> if I specify de disk like:
> disk   = [drbd:vappprtem01,hda,w' ]
> The Guest VM found the disk but this appear with zero size.
> As far what I read the second way is the correct to live migration
> work without any race condiction...
> This link say that centos has a problem with block-drbd script
> provided by drbd, is anybody aware of that ?
> http://lists.xensource.com/archives/html/xen-users/2008-08/msg00176.html
> Any hints ?

Just specify the drbd devices directly as:

disk = ['phy:/dev/drbd0,hda,w' ]

And you should be ok. There is no need to use the scripts.

Be sure you don't specify the underlying device, but the drbd device!

Using the underlying device will cause the replicas to become
out-of-sync as what is written to the underlying device will
not be replicated and a consistency check will bring your drbd
resources offline!

You are also going to want to use the multi-master as master-slave
is too difficult to get to work properly between xend and heartbeat!


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