Hi --
I used to run two mailservers with identical MX priorities (poor man's
fail-over approach) with Maildir mail folders accessed by Dovecot.
Synchronization has been achieved using unison, mirroring all files except
dovecot index files.
Once in a while some oddities could be observed, like reappearing of deleted
mails, duplicates and such alike. But the all-over performance was quite good.
Then I wanted to migrate to mdbox, and I became interested in dsync. I did start
with 2.0.16 a couple of month ago, and recently upgraded to 2.0.18.
My experience with the 2.0.x dsync version is as follows (synchronization time:
every minute):
-- As long as mail is not stored in corresponding mailboxes at both servers at
the same time, all mailboxes become synchronized perfectly well, and no oddites
like reappearing of deleted mails or generation of duplicates can be observed.
-- If mail is stored into corresponding mailboxes at both servers simultaneously
in between two synching runs, it gets worrying.
-- If I do run dsync without '-f' those two mailboxes end up in becoming
asynchronous.
-- If I do run dsync with '-f' both mailboxes will become synchronized
let's say in 95% of all synchronization runs. BUT in 5%, I do experience
asynchronicity. Here a 'doveadm force-resync' sometimes works, but not
always, what worries me a lot.
-- I can see the missing mail in the mdbox storage file using UNIX' little
helpers but not with the help of dovecot tools. (Or I was unable to use them
properly.)
-- Modifying MX priorities in a way, that I do now have a primary and backup
mailserver scenario, very much reduced the risk of losing legitimate mail.
-- But sometimes I do lose some syslog mail being produced at the same time.
Therefore I modified runtimes in way to omit synchronicity.
Ok, I could have lived with that, but I was anxious to learn, if 2.1.x dsync
would perform better ;-)
Here my observations sofar (synchronization time: every minute):
-- No losses sofar using 'doveadm sync' with '-f'
-- A *lot* of reappearing deleted mails or mails moved from one mailbox to the
other.
-- Quite often I am unable to delete those mails using client functionality
(Mail.app, Roundcube).
-- In those cases one needs to stop synchronization, run 'doveadm
force-resync', delete all reappearing mail (quite a lot sometimes), empty
'Deleted' folders, and finally run 'doveadm purge'.
-- Running of 'doveadm sync' without '-f' doesn't improve
the situation. Still I do have to struggle with reappearing mails, and sometimes
with appearing duplicates.
-- I do have a test setup running for 24 hours now, where I do generate test
mails in a 6 minutes interval at both servers. Mails become synchronized
perfectly well, irrespectively if '-f' is set or not. This is a major
improvement to 2.0x. dsync (sofar).
-- But running the synchronization without '-f' still shows a *lot* of
reappering mail, though.
I do have the feeling that dsync became very much improved with regard to
missing mail in synchronization, good. But those reappearing mails make me think
about switching back to 2.0.x dsync and live with the drawback of preventing
mail to arrive synchronously at both servers.
Is someone out there experiencing a similar behaviour with dsync 2.1.x regarding
reappearing, thus indelible mail?
Regards,
Michael
