[DRBD-user] Three node cluster?

Arnold Krille arnold at arnoldarts.de
Tue Apr 17 12:05:28 CEST 2012

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Hi,

On 15.04.2012 22:05, Björn Enroth wrote:
> I am looking for information of how to deal with a KVM three node cluster
> with DRBD
> I have a "baby machine" ubuntu 11.10 pacemaker/drbd cluster with two nodes,
> local disks with drbd setup in between. This is working flawless.
>
> My challenge now is that I want to add a third node with the same setup.
> How do I handle drbd in this setup? I'd like to have all nodes active, to
> be able to migrate resources, mainly kvm virtual guests, around the cluster
> as I see fit. I'd also like pacemaker to be able to dynamically handle the
> load.

While drbd is great, this is exactly our intended use-case and also 
exactly the reason I am looking at other storage solutions. drbd can't 
do more than two nodes.

You can of course distribute the drbd-resources so that some are n1/n2, 
some n2/n3 and some n1/n3, but that becomes an administrators nightmare. 
And once you decide that you need four nodes with the data present on at 
least three nodes, you are stuck.
You can layer the drbd-resources but that is more meant for semi-distant 
mirrors and manual fail-over.
And if you want live-migrations for your vms with more then two primary 
filesystem nodes...

I am currently looking at glusterfs, there is also moosefs and ceph(fs), 
but only the first is meant to be stable enough that redhat gives 
commercial support for it. There are also other distributed cluster 
filesystems like lustre, but they lack redundancy.

Have fun,

Arnold
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