dovecot - Mar 2021 - How to dimension hardware when using replication?

Hello Postmaster,

for a decade we have been using Dovecot successfully as IMAP server at 
Augsburg University.

Now we face the decision to switch from separated SAN storage to 
mirrored SAN storage by means of the usual combination of dovecot 
director and dovecot replicator (CentOS 7, Dovecot 2.2.36).

Dovecot director runs on four virtual machines (4 cores, 4 GB memory). 
The replicated storage is handled by two HP servers with 2 Xeon(R) CPU 
E5-2620 (6 cores) and 32 GM memory. The network relies on 2 x 1 GBit 
Ethernet bond and two redundant 4 GBit SAN-fabrics.

Our concerns, (1) is this equipment suitable? We are talking here about 
25.000 mail accounts (LDAP) with 7 TB mail storage (mdbox) and in peak 
periods 10.000 parallel Dovecot processes and (2) what are adequate 
settings for director_user_expire, replication_max_conns and 
replication_full_sync_interval?

Loosing mails is unacceptable as well as users stumbling upon mails with 
the recent flag set which were read and deleted yesterday.

Who is using dovecot director and replicator and is willing to share 
settings and operational experience?

Thanks in advance

++ Michael Westerburg

-- 
Dr. Michael Westerburg

Universit?t Augsburg
Rechenzentrum
86135 Augsburg

Telefon 0821/598-2004
Telefax 0821/598-2028
michael.westerburg at rz.uni-augsburg.de
https://www.rz.uni-augsburg.de