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

Digimer linux at alteeve.com
Fri Jan 7 14:12:12 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 01/07/2011 03:36 AM, Felix Frank wrote:
>> The risk here, though, is with split-brains.
>> Consider this;
>> You have two partition on your DRBD; one each for two VMs. In the course
>> of normal operation you have one VM running on NodeA and the other VM
>> running on NodeB. DRBD Primary/Primary will allow this. Then though, you
>> have a split brain.
>> At the moment of the split brain, unless you've configured a stonith
>> device in DRBD, either side will go off on their own and your VMs will
>> continue to run. From this point on, both sides are "more up to date"
>> than the other. This is because both are writing to their VM's partition.
> <snip>
> Wasn't the intention to have one LV+DRBD per VM?
> Doing dual-primary have the nodes work with distinct parts of the same
> DRBD doesn't sound like much of a good idea, because of the scenario you
> described.
> It *is* a good idea to allow dual-primary when using one LV per VM
> though, so that live-migration is available, afaik.
> Regards,
> Felix

You are right. If you have one DRBD resource per LV/VM, then you will
avoid the scenario I described.

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