[Dovecot] nfs director

[Edward avanti]

On Fri, Aug 27, 2010 at 9:31 AM, Timo Sirainen <tss at iki.fi> wrote:

> On 26.8.2010, at 23.54, Edward avanti wrote:
>
> > Please can you explain why this is advantage over a hardware load
> balancer.
>
> It guarantees that the same user is accessed via the same server. Hardware
> LB can at best assign the connections from the same IP to the same server
> (but not e.g. new mail deliveries, or if user has multiple clients like
> home/work/mobile, or simply accesses webmail at the same time as has a
> client open).
>
>
But how does it help when new mail arrive on one of the 24 SMTP server,
where there can be no direction that I can see. You might control where user
login to get mail, but not which server accept mail.


> > I fail to see advantage if anything it add in more point of failure, with
> > several hundred thousand user, we can ill afford to mess around or add to
> > complexity, sometime keeping it simple is simply way to be, when use
> > qmail/vpopmail, we never had one failure or problem, ever, we very proud
> of
> > this record so our users.
>
> Are you using Dovecot? For how long? Do you see any errors in your logs?
>
> for not very long, few month.


> > if director service assign 60K user to each front end,  how it handle if
> 5K
> > simultaneous user login, but all 5K happen to be assign to that one
> machine,
> > it do all work whilst other 7 server sit there do nothing negating what
> the
> > LB is design for?
>
> The users are distributed based on the MD5 hash of their username and that
> gives a pretty good distribution of where the users go. Unless 5k of your
> users suddenly decide to coordinate such attack, I doubt you'll ever see
> anything even close to that happening. But sure, there is some variation. I
> don't have any real world numbers, but my guess is it's normally less than
> 20%.
>
>
there is a reason we have 8 pop server, in evening, pop mail is very busy by
many user, many server often have thousand of concurrent user session but
not multiple session per user.


> Also with some more work it would be possible to dynamically adjust how
> many new users are getting assigned to servers, but I wasn't planning on
> implementing that unless it becomes clear that it's needed.
>
> > Is it really worth it? Do we really need this, or just let foundry switch
> > handle it as it does now.
> > We also have 24 front end SMTP server, these deliver mail to netapp
> filer,
> > all 24 plus 8 pop3 server and 2 webmail imap server all mount /vmail, so
> all
> > access same maildir. it seem work very effective thus far and for many
> many
> > year when we use qmail and vpopmail.
>
>
> If you don't mind random Dovecot errors about index corruption I guess
> you're fine with how it works now. I guess your mails are delivered to
> maildirs by qmail? If you ever switch to Dovecot LDA you'll probably start


we have convert many qmail to postfix, sunday morning we plan migrate
remaining 14 to postfix.


> getting more errors. And if you ever plan to switch to dbox format then at
> latest you'll need director.




So this all because of index? what is ramification for user if this
corruption occur?
is it self healing over new pop or delivery?
Can index be disable?
We thought using dovecot deliver, but this seem not good idea now? As
dovecot not know how qmail or postfix put mail in, since just put it in, can
not dovecot deliver work same? or have only dovecot on pop3 server update
index?