Dear Joel,
Thank you for your response!
I installed DRBD 9.2.12 and retested, but the issue persists.
I think the logic of this problem is quite clear. First, an Inconsistent
replication serving as a sync target can be promoted to the primary when it is
connected to an uptodate replication. Next, if the connection with the primary
node is lost, the uptodate replication becomes outdated. Finally, after the
network is restored and synchronization is completed, the sync target updates
its metadata to match the sync source, which causes its state to also become
outdated.
Would it be possible to introduce a parameter that allows users to prevent the
promotion of Inconsistent replications? This could help avoid the the issue. If
you have other solutions, that would be great as well, of course.
Additionally, are there other methods to remove the outdated tag from the
metadata, aside from using the primary --force command?
Looking forward to your suggestions.
Best regards,
Rui
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????: Re: Issue with Both Diskful Nodes Being Outdated in DRBD9
Hello Rui,
Thank you for the clear report.
> I am using DRBD 9.2.8
Please test again with DRBD 9.2.12. There have been some improvements
in this area since DRBD 9.2.8 such as:
44cb5fa46478 drbd: Avoid wrong outdates in far_away_change()
It is possible that the problem you have discovered is fixed by that
commit, or by another related one.
> 1. Is it possible to configure DRBD to disallow the promotion of an
"Inconsistent" node to primary? This would help avoid this issue.
No, this is an important feature of DRBD. It should be possible to
promote a node whenever it has access to UpToDate data.
> 2. If both disked nodes are in the "outdated" state, is it guaranteed that
their data is consistent? If the data is consistent, it would it be safe to use
the --force option to promote one of the nodes to primary to resolve the
situation.
Outdated data is always consistent. So yes, you can use "primary
--force" to promote one of the nodes. In this particular situation,
the data is actually up-to-date, so "primary --force" is the correct
way to fix the DRBD state. In other situations, using "primary
--force" on an Outdated node will cause divergent data (split-brain).
> 3. Can nodes in the "Inconsistent" or "Outdated" state participate in
voting? Based on my understanding of distributed systems like etcd, unhealthy
nodes are not allowed to vote or become leaders.
It's complicated. Explaining the details of the quorum algorithm is
beyond the scope of this message. For a discussion of some of the
details, see:
https://linbit.com/blog/drbd-quorum-implementation-updates/
Best regards,
Joel
