[Dovecot] nfs director

Cor Bosman cor at xs4all.nl
Wed Sep 1 20:17:46 EEST 2010

Hi Noel, if you dont need the director, then thats great right? Why does
anyone need to justify anything? Just dont use it, end of discussion.  Those
of us that do have a need for it, can use it anyways. Even without your
agreement? Is that such a big problem?

> we have a some total of 2 imap servers, only used for webmail, so it is
> not a problem for us, at all, period.


> imap access is not common in this country, it is in fact extremely rare,
> common only for webmail servers.

It's common here. We have tens of thousands of direct imap connections,
and they're often from the same user. Seeing 3 or more connections from the
same user on different remote IP numbers is not uncommon.

> not an issue as I previously stated (twice I believe) as we do not
> permit multi session logins

Not for you perhaps, but it is for us, and it is for others. So im glad you
dont have this issue, we do, and the director solves it. No need to bash
the director service just because you dont like it.

> > dovecot LDA, which also wants to update the index files). Because of issues
> funny how postfix doesnt have this issue, qmail doesnt have this issue
> nor does exim (never ran sendmail in this config only a crazy person
> would use mbox over NFS)

We dont use mbox. We use maildir. I agree only a crazy person would use mbox
in a large scale environment.

Postfix has this issue as well. So does qmail. So does exim. It has nothing
to do with the software being used. It is a problem in the NFS protocol.
(it's not a locking issue as I mentioned, but a caching issue as timo
corrected.. i knew that, but in my haste to respond had locking in my mind.
same principle applies. Multiple servers accessing the indexes can cause
corruption due to inherent problems in the NFS protocol).

The reason you dont see this, is because you dont allow simultaneous logins
and dont offer direct imap access. Lets have this discussion again once you
offer that :)

> there certainly is a workaround, its called, in our case, use postfix's
> deliver, which under my instruction has already happened on half the
> servers since it is clear this issue will not ever be solved in dovecot.

Good for you. Im happy it works for you. 

> yes, this has been mentioned some 40 times already, you know, i do
> actually know this, however that will NOT solve the problem as outlined
> earlier, the director by Timos admission will NOT load balance users in
> its current state, nor will it load balance inbound connections.

Huh? Guess I dont understand what you outlined earlier. The director does
load balance users. It uses an MD5 hash to do this, which in theory could
cause uneven loadbalancing, but I know for a fact that in practice it
poses no problem as we've been using an MD5 hash to loadbalance our webmail
frontend to our imap servers for years. Thats 20.000+ simultaneous users
and they get very evenly spread.

Maybe I just dont understand what your issues with other people using the
director are. If you have a solid system without the director, more power
to you. Thats great. Congrats.



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