[Dovecot] Performance of Maildir vs sdbox/mdbox

[Lee Standen]

Hi Guys,

 

I've been desperately trying to find some comparative performance
information about the different mailbox formats supported by Dovecot in
order to make an assessment on which format is right for our environment.

This is a brand new build, with customer mailboxes to be migrated in over
the course of 3-4 months.

 

Some details on our new environment:

* Approximately 1.6M+ mailboxes once all legacy systems are combined

* NetApp FAS6280 storage w/ 120TB usable for mail storage, 1TB of FlashCache
in each controller

* All mail storage presented via NFS over 10Gbps Ethernet (Jumbo Frames)

* Postfix will feed new email to Dovecot via LMTP

* Dovecot servers have been split based on their role

  - Dovecot LDA Servers (running LMTP protocol)

  - Dovecot POP/IMAP servers (running POP/IMAP protocols)

  - LDA & POP/IMAP servers are segmented into geographically split groups
(so no server sees every single mailbox)

  - Nginx proxy used to terminate customer connections, connections are
redirected to the appropriate geographic servers

* Apache Lucene indexes will be used to accelerate IMAP search for users

 

 

Our closest current live configuration (Qmail SMTP, Courier IMAP, Maildir)
has 600K mailboxes and pushes ~ 35,000 NFS operations per second at peak 

 

Some of the things I would like to know:

* Are we likely to see a reduction in IOPS/User by using Maildir alone under
Dovecot?

* What kind of IOPS/User reduction could we expect to see under mdbox?

* If someone can give some technical reasoning behind why mdbox does less
IOPS than Maildir?

 

I understand some of the reasons for the mdbox IOPS question, but I need
some more information so we can discuss internally and make a decision as to
whether we're comfortable going with mdbox from day one.  We're very
familiar with Maidlir, and there's just some uneasiness internally around
going to a new mail storage format.

 

Thanks!