On Tuesday 17 April 2012 10:08:33 you wrote: > On Tue, Apr 17, 2012 at 3:05 AM, Arnold Krille <[email protected]> wrote: > > 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. > > FWIW, I agree that GlusterFS is probably the best available option at > this time, for this use case. I'd recommend Ceph (Qemu-RBD, > specifically) if the virtualization cluster was larger, but the > GlusterFS option combines excellent ease-of-use with good redundancy > and would probably be your best bet for this cluster size.
Afaik ceph can do replication of the kind "give me three replicas, no matter how many backend-nodes are up". A feature gluster is missing in the current stable version (but I've been told that its coming in 3.3, due next months). I like the rbd-device interface of ceph, but during my tests with ceph during this last winter (yes, the whole week!:) ceph died on me two times and took its data with it. glusterfs also has problems when the participating nodes change ip-addresses, but still all the data is accessible... But all these technologies are fairly new, no one yet has found the ultimative solution to the split-brain-problem for example, and so your milage may vary... A sidenote to get back on topic: While my co-admin had his small victory some months ago, when it was decided to go back from drbd-hosting to his extra- iscsi machine, last week that machine had a problem starting after an power- outage. The only vm running fine was that last (and un-important) vm coming from drbd... Have fun, Arnold
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