Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Digimer wrote: > > On 01/07/2011 04:00 PM, Lentes, Bernd wrote: > > VM1A and VM1B are identical VM's, offering the same service ! > > Here is the confusion. When you say "identical", you are > referring to the underlying data being mirrored on both > nodes, right? That is, one VM > (VM1) that runs on *either* Node 1 *or* Node 2, right? I mean both: the data is identical (that's the purpose of DRBD) and so, of course, the vm's are identical. > > If you are thinking of two separate instances, however, that > is not possible. > > "Otherwise, yes, that would work perfectly." I don't understand what you mean here. > > > The vm's are installed in the plain DRBD, without any > filesystem. Each vm has just to be created once, because > DRBD, responsible for the replication, takes care that the vm > "appears" > > on the other node. Right ? Is DRBD able to replicate that, > although there is no filesystem ? > > Yes. DRBD is a block device level application. It doesn't > care at all about what might be using it. Think of DRBD as > just another hard drive. > > > Is this scenario senseful ? > > Yes. > > > In this scenario, is it possible to run VM1A and VM1B > simultaneously, in a DRBD dual primary mode ? I don't think so. > > I hope my scenario is clear. > > Absolutely not. :) > > VM1 is VM1. It's data will always be identical on both nodes, > but only one node will actually be hosting the VM at any one > time. Trying to start it up on the second Node would be a > *very* bad idea. > > Remember; > > Should you run into a split brain, you will need to manually > run 'drbdadm invalidate rX' on the node that the VM was /not/ > running on. > Let's say that VM1 (DRBD r1) and VM3 (DRBD r3) were running > on Node 1 and VM2 (DRBD r2) was running on Node 2. Now the > DRBD resources split-brain (ie: network fault). You would now > need to run: > > Node 1: > - drbdadm invalidate r2 > > Node 2: > - drbdadm invalidate r1 > - drbdadm invalidate r3 > > Once that is done, you could reconnect and the DRBD resources > would re-sync. Does this make sense? Now things are becoming clearer. I try to avoid split brain by using two ethernet adapters on each node, combining them in a bond device. Bernd > > -- > Digimer > E-Mail: digimer at alteeve.com > AN!Whitepapers: http://alteeve.com > Node Assassin: http://nodeassassin.org >