----- On Jun 7, 2016, at 5:54 PM, Digimer li...@alteeve.ca wrote:
> DLM is just a distributed lock manager, that's it. LVM uses it to > coordinate actions within the cluster, so what LVM does is still up to LVM. > > I'm not a dev, so I might get this a little wrong, but basically it > works like this... > > You want to create an LV from a clustered VG. The dlm and clvmd daemons > are running on all nodes. You type 'lvcreate ...' on node 1. Node 1 asks > for a lock from DLM, DLM checks to make sure the lock your asking for > doesn't conflict with any locks held elsewhere in the cluster and then > it is granted. What is locked ? The metadata (information about PV, VG, LV) ? Or the access to the LV ? > > Now the local machine creates the LV (same that no one else is going to > work on the same bits because of the DLM lock), releases the lock and > informs the other nodes. The other nodes update their view of the VG and > see the new LV. > > From the user's perspective, the LV they created on node 1 is instantly > seen on the other nodes. > >> >> But maybe i want to have some vm's running on host A and others on host B. >> Remember: one vm per LV. >> So i need access to the VG concurrently from both nodes, right ? >> But if the FS from the LV is a cluster ressource, pacemaker takes care the >> the >> FS is mounted just from one node. >> I can rely it on it, right ? That's what i read often. >> But what if i don't have a FS ? It's possible to have vm's in plain >> partitions, >> which should be a performance advantage. > > Clustered LVM doesn't care how an LV is used. It only cares that changes > won't conflict (thanks to DLM) and that all nodes have the same view of > the LVM. So deactivate, activate, grow, create, delete of PVs, VGs and > LVs are always seen on all nodes right away. > > What you do on the LVs is up to you. If boot a VM on node 1 using an LV > as backing storage, nothing in LVM stopping you from accessing that LV > on another node and destroying your data. That's logical. But the VM will be a ressource so the cluster manager takes care that only one instance of the VM is running anytime. Bernd Helmholtz Zentrum Muenchen Deutsches Forschungszentrum fuer Gesundheit und Umwelt (GmbH) Ingolstaedter Landstr. 1 85764 Neuherberg www.helmholtz-muenchen.de Aufsichtsratsvorsitzende: MinDir'in Baerbel Brumme-Bothe Geschaeftsfuehrer: Prof. Dr. Guenther Wess, Dr. Alfons Enhsen, Renate Schlusen (komm.) Registergericht: Amtsgericht Muenchen HRB 6466 USt-IdNr: DE 129521671 _______________________________________________ Users mailing list: Users@clusterlabs.org http://clusterlabs.org/mailman/listinfo/users Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org