[Dovecot] Maildir Subsystems

[Timo Sirainen]

On Feb 22, 2008, at 8:23 PM, Aaron Wiebe wrote:

> 1.  We customize our maildir system fairly heavily, and I'm wondering
> where the maildir code is located.  Specifically, anywhere the app
> actually does work on disk related to folders, mail content and
> quotas.  While I have reviewed the code in brief, I thought it would
> be easier to poke this list to get pointed in the right direction.

src/lib-storage/index/maildir/ has all the maildir specific code. In  
v1.1 the mailbox listing is separated from mailbox storage handling to  
src/lib-storage/list/. A lot of code is common between all mailbox  
backends though.

Quota is implemented as a plugin in src/plugins/quota/ and src/plugins/ 
imap-quota/.

> 2.  Courier works quite well over NFS for us, and I'm curious why your
> documentation covers NFS more specifically.  What aspects of the
> filesystem are normally used that don't translate easily to work over
> NFS? Do you use stuff like inotify or atimes?

inotify is used, but not relied on. The main problem anyway with NFS  
is its caching. If two servers modify the same mailbox at the same  
time, they may return data to Dovecot that had already been changed by  
another server. This is more of a problem with Dovecot than with  
Courier because Dovecot does more complex file handling than Courier.  
Especially Dovecot's index files give easily problems if caching works  
unexpectedly.

Dovecot v1.1 handles NFS a lot better than v1.0 and I'd suggest not  
bothering with v1.0 anymore if you use NFS.

> 3.  If anyone has any suggestions on how to migrate tens of thousands
> of imap users from courier to dovecot in a few hour window, I'd like
> to hear them :)

1) Call Courier migration script (http://wiki.dovecot.org/Migration/Courier 
) from post-login script (http://wiki.dovecot.org/PostLoginScripting)  
for the user logging in.
2) Stop Courier
3) Start Dovecot

Downtime: a couple of seconds. :)
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