Verifying replication

[Arnold Hendriks]

Dear Dovecot people,

I've set up Dovecot replication a couple of years ago. I'm watching the
general server health and having Nagios check doveadm replicator status
regularly. I'm seeing accounts replicating, disk space usage obviously
shows that things work in principle, however, I still wonder whether the
replication actually works properly. Accounts I check work, but 1-5% of the
messages could easily be missing without me noticing it. These servers have
I think about 50K accounts (a lot of them dormant) and between 1 to 2TB of
mail.

I'm trying to get some more confidence as to whether replication is
actually working properly and whether I'm not missing anything that will
burn me if I ever have to 'fallback'. Has anyone ever done some
verification outside of simply watching doveadm replication stats, to see
if they are missing anything ?

Eg, I could imagine a process that generates a list of accounts, and
then generates hashes on both sides of the replication for each mailbox
folder. If the hashes match, the folder gets removed from the list, and
once all folders are removed, the account gets removed. Iterating the
account list should finally reduce it to 0, or a few extremely high traffic
accounts which can be checked manually or be ignored.

But I'm trying to avoid reinventing the wheel. Has anyone done anything
like this, or can suggest a different approach?

With regards,
Arnold Hendriks
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