migration with doveadm backup to new cluster running dovecot 2.2.36 and replicator

Thomas Winterstein thomas.winterstein at rz.uni-augsburg.de
Wed Dec 23 21:33:48 EET 2020

Hello everyone,

we are working on migrating from dovecot 2.0.9 (maildir) to 2.2.36 
(mdbox). The new cluster has two backend mail servers which replicate 
through doveadm replicator. To move the data initially we use doveadm 
backup (imapc).

Our migration command
  doveadm -o mail_fsync=never backup -R -u $user imapc:

To test the replication of new and purge of old mails with live data 
changes we ran imapc on a daily basis but encountered the problem that 
some mailboxes multiplied in size. We then made sure that imapc and 
replication don't run at the same time but after the first incremental 
imapc process, we still had the same problems.

The doveadm-backup man-page states that it's possible to run it multiple 
times during migration. But is it also possible to have the replicator 
running in between? From our understanding the doveadm backup should 
just work as an imap connection between the servers, synchronizing all 
changes made on the source to the destination. Or does the conversion 
from maildir to mdbox format in our case produce the problems?

If you're not supposed to run the replicator before having fully 
migrated, how can we shorten the downtime? rsync? And how can we be sure 
that similar problems don't occur after the migration if we can't test 
all mechanisms together with live data?

Thomas Winterstein

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