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drbd-user: Re: [DRBD-user] becoming primary with outdated data

Re: [DRBD-user] becoming primary with outdated data

From: Alex Dean <alex_at_nospam>
Date: Tue Mar 23 2010 - 15:46:43 GMT
To: Lars Ellenberg <lars.ellenberg@linbit.com>

On Mar 23, 2010, at 9:16 AM, Lars Ellenberg wrote:

> On Mon, Mar 22, 2010 at 09:39:00AM -0500, Alex Dean wrote:
>> I'm using drbd 3.3.7 + heartbeat 3. I've configured dopd using
>> http://www.drbd.org/users-guide/s-heartbeat-dopd.html. It works as
>> expected. If I pull the ethernet cable used for drbd replication, I
>> see dopd activity in heartbeat's logs, and the secondary's dstate
>> changes to 'Outdated'.
>>
>> Is it somehow possible to force drbd to become primary with this
>> outdated data? I'm thinking if there is an unnoticed (failure of
>> monitoring, perhaps?) failure of the replication link, and then
>> there is some catastrophic failure on the primary which renders its
>> data unusable, it might be preferable to go forward with promoting
>> the outdated secondary to primary status. I understand this means
>> lost data.
>>
>> I've been reading through the man pages for drbdadm and drbdsetup,
>> as well as the DRBD Users Guide, and haven't found anything
>> describing how to do this. Can it be done?
>
> Prior to 8.3.8, you'd have to fiddle with drbdmeta set-gi.
> Starting with drbd 8.3.8 (which has not been released yet,
> so read "current git", if you like) a simple --force primary
> will do.

Thanks for the reply.

I've configured dual NICs for DRBD replication in active/passive
bonding, so I think the hypothetical situation I described is
unlikely. But I've seen other 'unlikely' things occur. Just trying
to think through what the failure scenarios are, and how we'd recover
from them.

alex

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