----- On Jun 7, 2016, at 11:52 PM, Ferenc Wágner wf...@niif.hu wrote: > "Lentes, Bernd" <bernd.len...@helmholtz-muenchen.de> writes: > >> ----- On Jun 7, 2016, at 3:53 PM, Ferenc Wágner wf...@niif.hu wrote: >> >>> "Lentes, Bernd" <bernd.len...@helmholtz-muenchen.de> writes: >>> >>>> Ok. Does DLM takes care that a LV just can be used on one host ? >>> >>> No. Even plain LVM uses locks to serialize access to its metadata >>> (avoid concurrent writes corrupting it). These locks are provided by >>> the host kernel (locking_type=1). DLM extends the locking concept to a >>> full cluster from a single host, which is exactly what cLVM needs. This >>> is activated by locking_type=3. >> >> So DLM and cLVM just takes care that the metadata is consistent. >> None of them controls any access to the LV itself ? > > cLVM contols activation as well (besides metadata consistency), but does > not control access to activated LVs, which are cluster-unaware > device-mapper devices, just like under plain LVM. > >>>> cLVM just takes care that the naming is the same on all nodes, right? >>> >>> More than that. As above, it keeps the LVM metadata consistent amongst >>> the members of the cluster. It can also activate LVs on all members >>> ("global" activation), or ensure that an LV is active on a single member >>> only ("exclusive" activation). >>> >>>>>> Later on it's possible that some vm's run on host 1 and some on host 2. >>>>>> Does >>>>>> clvm needs to be a ressource managed by the cluster manager? >>> >>> The clvm daemon can be handled as a cloned cluster resource, but it >>> isn't necessary. It requires corosync (or some other membership/ >>> communication layer) and DLM to work. DLM can be configured to do its >>> own fencing or to use that of Pacemaker (if present). >>> >>>>>> If i use a fs inside the lv, a "normal" fs like ext3 is sufficient, i >>>>>> think. But >>>>>> it has to be a cluster ressource, right ? >>> >>> If your filesystem is a plain cluster resource, then your resource >>> manager will ensure that it isn't mounted on more than one node, and >>> everything should be all right. >>> >>> Same with VMs on LVs: assuming no LV is used by two VMs (which would >>> bring back the previous problem on another level) and your VMs are >>> non-clone cluster resources, your resource manager will ensure that each >>> LV is used by a single VM only (on whichever host), and everything >>> should be all right, even though your LVs are active on all hosts (which >>> makes live migration possible, if your resource agent supports that). >> >> Does the LV need to be a ressource (if i don't have a FS) ? > > No. (If you use cLVM. If you don't use cLVM, then your VGs must be > resources, otherwise nothing guarrantees the consistency of their > metadata.) > >> From what i understand from what you say the LV's are active on all >> hosts, and the ressource manager controls that a VM is just running on >> one host, so the LV is just used by one host. Right ? So it has not to >> be a ressource. > > Right. (The LVs must be active on all hosts to enable free live > migration. There might be other solutions, because the LVs receive I/O > on one host only at any given time, but then you have to persuade your > hypervisor that the block device it wants will really be available once > migration is complete.) > -- > Feri
OK. I think i got it now. Thanks for the help. 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