[Drbd-dev] Re: drbd Frage zu secondary vs primary; drbddisk status problem

[Lars Marowsky-Bree]

On 2004-08-20T15:32:15,
   Lars Ellenberg <Lars.Ellenberg at linbit.com> said:

>   N1    N2
>   P --- S   Everything ok.
>   P - - S   N1 is failing, but for the moment being just can no
>             longer answer the network; but it is still able to update
>             drbds generation counts
>   ?   - S   Now N1 may be dead, or maybe not
>   X   - S   A sane Cluster-mgr makes N2 primary, but stonith N1 first ...

As you pointed out, the sane cluster manager (or admin) ought to be
setting a Kain flag when it knows for sure it has slain it's brother...

Now, that would even help catch the case where the crm had a malfunction
and made both sides primary, in which case it really really shouldn't
automatically connect, but will require higher level help (to make one
side secondary first).

>   X   - P   N1 now is really dead.
>   S --- P   N1 comes back
>   S - : P   oops, N1 has "better" generation counts than N2
>             N2 shall become sync target, but since it is
>             currently Primary, it will refuse this.
>             It goes standalone.
> 
> Now, I think in that case, N1 needs special handling of the situation,
> too, which it currently has not.

> Yet an other deficiency:
> we still do not handle the gencounts correctly in this situation:
> 
>   S --- S
>   P --- S  drbdsetup primary --human
>    now, N1 increments its human cnt, N2 only its connection count after
>    failure of N1, N2 will take over, maybe be primary for a whole week.
>    then N1 comes back, has the higher human count, and will
>    either [see above] (if N2 still is Primary)
>    or wipe out a week worth of changes (if N2 was demoted to Secondary
>    meanwhile).
> 
>    Oops :-(

Ouchie. Probably should send that across the wire...


Sincerely,
    Lars Marowsky-Brée <lmb at suse.de>

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