On 11/4/2013 6:55 PM, Dimitri Maziuk wrote:
> On 11/04/2013 04:17 PM, Phil Stracchino wrote:
> ...  In at least one of the
>> cases I know about, though, the problem was not a failure of DRBD per
>> se, it was that someone accidentally started up mysqld on the second
>> node, which normally would not be allowed to happen because the second
>> instance accessing the same filesystem would not be allowed to lock the
>> InnoDB tablespace.  In the DRBD situation, though, there was nothing
>> whatsoever locking the tablespace on the local machine, so it quite
>> cheerfully allowed both mysqlds to write to their own local instances of
>> the tablespace on the replicated filesystem, whereupon the two mysqlds
>> proceeded to destroy the tablespace by making it internally inconsistent.
> Ah, the "active-active" setup. I agree: avoid like plague.
>
> The simple stupid (and bulletproof) setup is an active/passive cluster
> with drbd, mysql, and floating ip. Unfortunately if it fails over your
> bacula-dir is going to lost its connection to the db and kill the
> running backup -- see my post from 2 days ago.

And I think that will always be the case in a fail-over situation as 
long as Bacula requires the persistent network connection and fails jobs 
without attempting a reconnect. I think that Open vSwitch could allow 
live migration of DIR and SD without the connection loss, but not in a 
fail-over situation where the hardware has dropped the connection. That 
is why I said that Bacula is not entirely cluster friendly. That is not 
a deal breaker, since much of the tape hardware SD can use as backup 
devices require manually plugging the device into another node anyway. I 
have been running DIR and SD in a kvm VM on a 2-node cluster for a 
couple of years now without issue, other than it is not fail-over 
capable. I can run the VM on either node, though it requires manually 
migrating the VM. It would be nice if Bacula were fail-over capable, but 
still it works just as well running in a VM on a cluster as on bare metal.


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