[Dovecot] Multi Server Exim/Dovecot and NFS

[Robert Schetterer]

Am 16.07.2012 16:19, schrieb Robert Blayzor:

> 
> We're talking about tens of thousands of mailboxes and at least half a dozen servers involved.  There is quite a bit of traffic.  We've been running Maildir via NFS with another mailserver product for some time, and it's been ok as far as the shared file system standpoint.

jep ,thats a big setup

> 
> I don't know why Maildir would be "not ideal".  It seems to be the only option when it comes to NFS.

mdbox may be more performant

http://wiki2.dovecot.org/MailboxFormat/dbox

> 
> NFS is used extensively in our network and we already have a major investment with NetApp, and have been very happy with them.

i believe you, but good cluster file systems may better fit with imap

> 
> The only issue I see right now is Dovecot index file write bashing if a user accesses their mailbox from multiple locations at the same time, and I gave that example in the previous post.  That seems to be more and more common these days but still not the norm for 80%+ of the mailboxes we have.

in modern times, people use to have many clients open ,same time, over
imap i.e with mobiles comming over different ips, your setup solution
should honor this, indexes then may get a problem, which you have to
handle with

http://wiki2.dovecot.org/NFS

--snip
index files

If you keep the index files stored on NFS, you'll need to set
mmap_disable=yes. If you're not running lockd you'll have to set
lock_method=dotlock, but this degrades performance. Note that some NFS
installations have problems with lockd. If you're beginning to get all
kinds of locking related errors, try if the problems go away with
dotlocking.

With mbox/Maildir format it's also possible to store index files on
local disk instead of on NFS. If the user gets redirected to different
servers, the local indexes are automatically created/updated. If the
user is (nearly) always redirected to the same server this should be
fine and you would likely get higher performance than indexes stored on
NFS, but if the server changes it can be slow to recreate the
index/cache files.
--snip

> 
> From the MTA side of things, it looks like having Exim write directly into the ~/Maildir/new/ is the only sane choice since mail can be coming into a mailbox from a number of servers at the same time.  We've used this extensively in the past with no issues.

dont know exim, i use postfix lmtp, and a cluster file system storage
drbd, no failures so far

> 
> We use a Brocade ADX to load balancing POP and IMAP sessions to the server.

dont know  brocade, but good working loadbalancers is a must have , you
may also think about using directors additional

http://wiki2.dovecot.org/Director

shouldnt harm you

  Stickiness doesn't really buy you anything on POP3 since a session
connects, does it's thin and disconnects.  IMAP on the other hand, I
believe can have multiple connections open from the same client, so I
think sticky would help.  But neither of those help when the client is
connecting from a different IP address.
> 
> 
> Robert Blayzor
> INOC, LLC
> rblayzor at inoc.net
> http://www.inoc.net/~rblayzor/
> 
> 
> 

i think your setup is quite common, anyway it may not be ideal
i would recommand to hire dovecot specialist and/or Timos Company
directly to do consulting with such big setups



-- 
Best Regards
MfG Robert Schetterer