[DRBD-user] Automatic split brain recovery policies - after-sb-0pri - discard-older-primary

GAUTIER Hervé herve.gautier at thalesgroup.com
Wed Jan 7 12:23:11 CET 2009

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


Dominik Klein a écrit :
>> Ok, but, excuse me, as my english is far from perfect, I don't
>> understand very well the discard-older-primary policy for after-sb-0pri:
>> "Auto sync from the node that became primary as second during the
>> split-brain situation."
>>     
>
> Maybe an example can shed some light here.
>
> * nodes node1 and node2 are disconnect at Time t0.
> * At t1, node1 becomes primary.
> * At t2, node2 becomes primary.
> * At t4, both nodes are seconary again.
> * At t5, nodes are reconnected.
>
> Now after-sb-0pri (after split brain with currently 0 primaries), the
> "discard-older-primary" policy will make node2 the sync source, as it
> will discard the "older" primary (the node that became primary first).
>
> Regards
> Dominik
>   
Very clear !
Many thank !

I don't understand why this policy is very rarely used.
And in case of "discard-younger-primary" policy, node1 will be selected 
as the sync source. Am I right ?

In case of the following situation:

nodes node1 and node2 are disconnected
At t0, split brain
At t1, node1 becomes primary
At t2, node1 becomes secondary
At t3, node2 becomes primary
At t4, node2 becomes secondary
At t5, node1 becomes primary
At t6, node1 becomes secondary
At t7, node2 becomes primary
At t8, node2 becomes secondary
At t9, node1 becomes primary
At t10, node1 becomes secondary
At t11, node2 becomes primary
At t12, node2 becomes secondary
At t13, node1 becomes primary
At t14, node1 becomes secondary
At t15, node2 becomes primary
At t16, node2 becomes secondary
At t17, node1 becomes primary
At t18, node1 becomes secondary
At t19, node2 becomes primary
At t20, node2 becomes secondary
At t21, node1 becomes primary
At t22, node1 becomes secondary
At t23, node2 becomes primary
At t24, node2 becomes secondary
At t25, split brain is fixed

"discard-older-primary" policy will make node2 from t23 the sync source
"discard-younger-primary" policy will make node1 from t1 the sync sourc, 
or node1 from another time than t1 ?

Regards,

-- 
Hervé GAUTIER




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