[Dovecot] dsync replication questions

[Nikolaos Milas]

I am running two servers with Dovecot v2.2.12 on CentOS x86_64 (5.10 and 
6.5 respectively) and users are virtual over ldap.

I have setup our main internal server (vmail.example.com) with dsync 
replication according to the first part of 
http://wiki2.dovecot.org/Replication. The second one 
(vmail1.example.com) will be the failover server which we want to be a 
real-time mirror (but can be manipulated directly and it should 
propagate changes back to vmail.example.com).

When I started the server (vmail.example.com), mirroring started and 
completed fine (after a few hours).

However, since then, I am not seeing a continued mirroring between the 
two. I would expect changes to one of the masters to be propagated in 
real time to the other - which does not happen.

If I manually run (on vmail.example.com):

    dsync -u imaptester mirror ssh -l root vmail1.example.com dsync -u
    imaptester

then these two accounts are synced.

Question 1: Shouldn't mirroring continue automatically in real time 
(having configured it as in the first part of 
http://wiki2.dovecot.org/Replication)? If not, what should I do to 
enable such a real-time (or near-real-time) sync?

Note that I have not configured "replication_dsync_parameters" as noted 
at the above page.

Question 2: Where can I find documentation about 
"replication_dsync_parameters" and about "the doveadm sync command" 
(referred to at the same page)? I have not been able to locate such a 
documentation/wiki page.

Question 2a: What do options "-d -N -l 30 -U" signify in 
"replication_dsync_parameters = -d -N -l 30 -U"?

Thanks,
Nick