"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 _______________________________________________ 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