[DRBD-user] Can you tell me what happens in this hypothetical case?

Philipp Reisner philipp.reisner at linbit.com
Sat Feb 21 09:34:24 CET 2004


Am Samstag, 21. Februar 2004 00:35 schrieb Mark Hellman:
> Host A is primary, host B is secondary.
>
> Step    Time      Status/Events
> 1        00       A and B are up
> 2        90       B goes down, A remains up
> 3       180       A goes down
> 4       260       B comes up, A remains down
> 5       450       A comes up  (how is sync done?)
>
> Assuming that at step 4, host B started serving requests, then at the end
> of step 5 neither A nor B will have all the data up to date. This because
> tetween steps 2 and 3, files may have been created or modified on host A.
> And between steps 3 and 4, the same may have happened on host B.
> If any sync is done on step 5, in what direction will it occur?
>

It depends on your configuration and on your needs.

in the "datacenter scenario" you will have configured inittimout=0.
Then in step 4 B will _not_ become primary automatically. It will
stall the boot process before heartbeat start. --> No service
will be available. This is the datacenter scenario! Some operator
will be alerted by some monitoring system and have a look at 
B's console. And there it will find the infamous question

Do you want to abort waiting for other server and make this one primary?


In the "embedded scenario" you will have configured inittimeout=120.
Then in step 4 B will answer this question by itself with "yes",
become primary and therefore will have the "good" data. In
step 5 A's data will be overridden by B's data.

-Philipp



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