[Dovecot] o/s tuning for imap

[Kyle Wheeler]

On Tuesday, September  4 at 12:16 PM, quoth Ken A:
> I'm switching from a pop3 only dovecot install to a pop3/imap install and 
> I'm wondering how many connections every 100 'normal' imap users might 
> have/keep open?

Mmmm, I usually estimate that most of the time users keep one 
connection open. Occasionally some clients (like Mail.app with the 
IDLE plugin) keep two or three open at all times. Then of course, 
there's occasional bursts where a client may open ten or more 
connections, though because IMAP is asynchronous that's technically 
unnecessary unless you're doing it to reduce latency (unlikely), but 
some clients do it anyway.

So I'd leave a max of around 300-500 connections at minimum.

> I'm wondering if I need to tweak any o/s related things, like 
> time_wait, etc. Any pointers would be greatly appreciated.

The thing to keep in mind about IMAP versus POP is that more folks 
will be keeping things on your server. That means you're going to need 
more disk space and (particularly if you use a Maildir backend) more 
inodes, and you're going to want to reexamine your filesystem and 
mount options. For example, if you haven't already, turn off atime 
updating. It's entirely useless with Dovecot, and will just slow you 
down.

~Kyle
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