On 11/22/2011 12:38 PM, Ronney Meier - Rorotec Informatik GmbH wrote: >>> Hi all >>> >>> I have a 2 node setup with lvm on top oft wo drbd devices and two xen >> virtual machines running. >>> The pacemaker version used is 1.0.11 . >>> All of the resources should always be running on the same node. >>> This usually works, but last week after a crash it happened, that pacemaker >> made one of the drbd devices master on one node, and the other drbd >> device on the other node. So it couldn't bring up the lvm anymore and >> therefore also none of the other resources were able to run. >>> My colocation and order constraints look like that here: >>> >>> colocation xen_on_drbd inf: ( xen-windows_server_sb >>> xen-windows_server_standard ) fs-xendata lv-drbd_data ( >>> ms-drbd_r0:Master ms-drbd_r1:Master ) >>> >>> order ord-xen_after_drbd inf: ( ms-drbd_r0:promote ms-drbd_r1:promote >>> ) lv-drbd_data:start fs-xendata:start ( xen-windows_server_sb:start >>> xen-windows_server_standard:start ) >>> >>> So that it should first promote the two drbd devices, then den bringing up >> the lvm (=lv-drbd_data), then mounting the filesystem with the xen images >> (=fs_xendata) and then starting up the virtual machines. >>> Resources in the colocation constraint inside of parenthesis should be >> independent from each other. >>> >>> If I didn't completely missunderstood how the colocation of sets works, it >> should be impossible, that pacemaker promotes the two drbd devices on >> different nodes. >>> Or did I make an error with these constraints? >> >> Yes, you make an error ;-) ... if you set the parenthesis around resources >> you >> set the sequential attribute to false. For an order resource sets that means: >> unordered. For a colocation set it means: not colocated ... and that is what >> you saw in you setup. >> >> >> Remove the parenthesis around the DRBD masters in your colocation and >> everything should be fine. >> >> Are these two DRBD devices acting as two PVs for one VG? This is not a >> recommended setup because ... as you already saw ... the two DRBD master >> could end on different nodes or be disconnected individually having a >> different data generation in case of an failover and then you have serious >> problems with your VG. This can be handled properly in DRBD 8.4.x. that >> supports serveral volumes per connection. >> >> Regards, >> Andreas > > Hi andreas > > Thanks a lot for your answer. > > I was aware about what the sequential attribute means for an order resource... > From the documentation I understood that for the colocation attribute it > means that they are collocated, but don't depend on each other, so if one of > them doesn't run pacemaker will not also shoot down the other ones > (especially important for the virtual machines).
Setting the sequential attribute to false makes them unrelated to each other -- no colocation (or order) at all ... not unrelated to other resources within the set. > Ok, so I will take away the parenthesis, but just for further understanding: > If the parenthesis are around the drbd resources, it means they don't need to > be collocated with each other. But don't they still need to be colocated with > the lv-drbd_data resource? And since both of them need to be collocated with > this resource they implicitly also need to be collocated with each other? Or > pacemaker doesn't resolve this kind of implicit dependencies? (or another > misunderstanding from my site?) > It is the other way round all resources depend on the drbd:Master resources ... the order within colocation resource sets is like in groups ... the order between sets is like simple colocation constraints, not like in groups .... > Yes, these two drbd devices act as two PV for one VG. We didn't had enough > HDD space left, so we had to add more... > At least the problem with ending up on different nodes pacemaker should take > care of (if properly configured, ähm), but if they get disconnected > individually we'd had quite a big mess and I'm not even sure if the lvm > driver would notice that. Thanks a lot, I didn't think about that. I Will see > how I get drbd 8.4 running in debian... Why not extending the lower level device of the DRBD resource followed by a resize operation of DRBD? Regards, Andreas -- Need help with Pacemaker? http://www.hastexo.com/now > > ronney > > _______________________________________________ > Pacemaker mailing list: Pacemaker@oss.clusterlabs.org > http://oss.clusterlabs.org/mailman/listinfo/pacemaker > > Project Home: http://www.clusterlabs.org > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf > Bugs: http://bugs.clusterlabs.org
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