Issue with Both Diskful Nodes Being Outdated in DRBD9

[Joel Colledge]

Hi Rui,

This should be fixed by the following commit from Phil:
https://github.com/LINBIT/drbd/commit/d8214d47d13a4c9b5c8f8cae7989de7996983688

Please test it to ensure that it fixes your precise scenario.

Best regards,
Joel


On Tue, 7 Jan 2025 at 17:12, Joel Colledge <joel.colledge at linbit.com> wrote:

> Hi Rui,
>
> > 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 primary node is lost, the uptodate replication becomes outdated.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 state to also become outdated.
>
> I am able to reproduce the problem too now.
>
> > 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.
>
> I believe the correct fix is at step 5. of your original reproduction
> steps. Node B should know that A does not have access to any UpToDate
> data and so cannot complete any writes. So node B should not become
> Outdated.
>
> I'm not sure how the exact implementation would work. We may need to
> add more information to the two-phase commit packets to allow node B
> to reliably determine its disk state.
>
> The fix should also make sure that node A does not consider node B to
> be Outdated at this stage.
>
> > Additionally, are there other methods to remove the outdated tag from
> the metadata, aside from using the primary --force command?
>
> It should be possible with the "get-gi" and "set-gi" commands, but I
> recommend using "primary --force", because it is much simpler.
>
> Best regards,
> Joel
>
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