Les Mikesell wrote:
> Chris Robertson wrote:
>   
>> Les Mikesell wrote:
>>     
>>> Chris Robertson wrote:
>>>   
>>>       
>>>> Read it again.  :o)  Both the external XFS journal (logdev=/dev/drbd1) 
>>>> AND the data partition (/dev/drbd0) are DRBD mirrored.  It would be 
>>>> silly to have only one or the other saved in a DR scenario.
>>>>     
>>>>         
>>> Have you investigated/tested what happens if one end or the other 
>>> crashes or they lose connectivity for some period of time?   I think 
>>> drbd has some tricks to deal with that but I don't know how well they 
>>> work in practice.
>>>   
>>>       
>> Well, I ran the BackupPC server without a partner for more than 2 weeks 
>> without a hitch...
>>
>> Tell you what.  Let me just run downstairs and unplug the network cable 
>> from the mirror server.  :o)
>>
>> I'll send another note in a couple hours with an account of what 
>> happens, then I'll go re-plug it in and report further.
>>     

Well, that was (expectedly) a boring test.  The BackupPC server was 
running the BackupPC_nightly jobs when I pulled the mirror's net 
connection.  At the time there were no out-of-sync entries.  Upon 
network "break" the master reported "PingAck did not arrive in time" and 
the peer was marked as Unconnected.  Before plugging the mirror back in, 
the nightly job had finished.  A total of 860412K was marked as out of 
sync.  Plugging the network cable back in caused a resync to 
automatically run.  All is right with the world.

More fun would be to interrupt the synchronization during heavy access 
(during backups or trashclean).  Then mark the backup as Primary see if 
it mounts.

Perhaps a test for another day.  Truly I expect it would be akin to 
mounting after a crash.
> Thanks - I'm interested in the theory as well as the practice on this 
> but didn't really expect it to work very well so I haven't followed the 
> software for a while.  Does it have some kind of diagnostics to see if 
> the partners are fully in sync

Yes.  http://www.drbd.org/users-guide-emb/s-online-verify.html

Chris




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