[DRBD-user] DRBD and KVM for a HA-Cluster ?

Digimer linux at alteeve.com
Sat Jan 8 21:46:38 CET 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On 01/08/2011 11:32 AM, Lentes, Bernd wrote:
> 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.

Think of DRBD like RAID 1. Just because the data is duplicated does not
mean that you can run the OS twice. It's the same with DRBD... The thing
with DRBD is that the data *can* be available from both nodes. For
example, running a GFS2 partition on Primary/Primary would allow both
nodes to mount the DRBD partition.

So in short; A given VM on a given LV can be run on *only* one node at a

>> 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 rest of what you described would work.

>> 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

That is only one possible method of causing a split-brain. To truly
protect against a split brain, you must configure a fence/stonith device.

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