[DRBD-user] 3-node active/active/active config?

[Gianluca Cecchi]

On Wed, Nov 18, 2009 at 9:12 AM, Gianluca Cecchi
<gianluca.cecchi at gmail.com> wrote:
>
> On Wed, Nov 18, 2009 at 5:30 AM, Jiann-Ming Su <sujiannming at gmail.com> wrote:
>>
>> Can you give a brief explanation of why that is the case?
>>
>>
>> Is the problem the dual path?  What if a single path was used in some
>> stacked configuration where a drbd is used as a backing device for
>> another drbd share?
>>
>>
>> --
>> Jiann-Ming Su
>
> It is wrong from a conceptual point of view, because as Lars already explained, when you write on md0 of A, you are only writing on half md0 of B (left side) and half md0 of C (right side).
> So the other two md0 devices are not in sync with the original md0....
> HIH,
> Gianluca

Actually, based on your first post where you gave:

Noce A:  md0 (drbd0, drbd1)
Node B:  md0 (drbd0, drbd2)
Node C:  md0 (drbd1, drbd2)

also for C you are hitting left side, so correct explanation would be:
when you write on md0 of A, you are only writing on half md0 of B
(left side) and half md0 of C (left side)