After a loooong thread on the dovecot mailinglist,http://article.gmane.org/gmane.mail.imap.dovecot/55874, Timo finally asked this discussion was taken elsewhere and suggested this wiki-page.
As long as mail_fsync is not set to "never", and (local) filesystem should be equally reliable from data loss issues from dovecot usage. This is because dovecot (and most SMTP-servers) will not aknowledge a message as processed before fsync() returns sucessfully. To quote Timo:
"Success isn't returned to dovecot-lda or IMAP APPEND call until the mail has been fsynced. As long as the disk doesn't lie and the filesystem doesn't lie, there is zero data loss when fsyncing isn't disabled with Dovecot."
What about NFS? Cluster filesystems? Running with mail_fsync=never ?
Who need performance ?
= Future ideas ? =
RFC: grouped fsync() http://comments.gmane.org/gmane.mail.imap.dovecot/55173