Hashed or Calculated Maildirs

Hi,

I want to use a hashing mechanism (nhash) from my MTA (Exim)
to split up the 
users maildirs into subfolders.

The directory structure looks like this:
/var/mail/0/totty or /var/mail/126/bill

Here is the part from the Exim configuration:
file =
"/var/mail/${nhash_127:$local_part}/$local_part/INBOX&q
uot;

My problem is, that I haven`t got a clue how the imap daemon
deals with the
new directory structure.
Has courier an implemented hashing mechanism?

Many regards
Torsten 


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Torsten writes:

> Hi,
> 
> I want to use a hashing mechanism (nhash) from my MTA
(Exim) to split up the 
> users maildirs into subfolders.
> 
> The directory structure looks like this:
> /var/mail/0/totty or /var/mail/126/bill
> 
> Here is the part from the Exim configuration:
> file =
"/var/mail/${nhash_127:$local_part}/$local_part/INBOX&q
uot;
> 
> My problem is, that I haven`t got a clue how the imap
daemon deals with the
> new directory structure.
> Has courier an implemented hashing mechanism?

No.  Courier expects that you will provide each account's
home directory in 
your authentication database.  Whatever authentication
method you are using 
- /etc/passwd, LDAP, MySQL, or whatever, each account must
have its home 
directory defined and Courier will simply use whatever is
set in the account 
database.



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> No.  Courier expects that you will provide each
account's home 
> directory in your authentication database.  Whatever
authentication 
> method you are using - /etc/passwd, LDAP, MySQL, or
whatever, each 
> account must have its home directory defined and
Courier will simply 
> use whatever is set in the account database. 
Damned, I couldn`t put the exact home directory to the
database, because
of Exim (nhash) is calculating the folders.

The reason is that I`m asking for is that I want to setup a
huge server
with  over 20000 user maildirs.
Because of filesystem performance it is necessary to split
up the user
folders.
Do you know any other way to do this?
Or are these requirements not true (filesystem
performance)?

Many regards
Torsten


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Totty writes:

>> No.  Courier expects that you will provide each
account's home 
>> directory in your authentication database. 
Whatever authentication 
>> method you are using - /etc/passwd, LDAP, MySQL, or
whatever, each 
>> account must have its home directory defined and
Courier will simply 
>> use whatever is set in the account database. 
> Damned, I couldn`t put the exact home directory to the
database, because
> of Exim (nhash) is calculating the folders.
> 
> The reason is that I`m asking for is that I want to
setup a huge server
> with  over 20000 user maildirs.

Tell me it's 2,000,000 accounts, and I'll be impressed. 
20,000 is chump 
change.  Add a field to the LDAP directory, a MySQL table,
or whatever you 
choose for your authentication back end, and put each
account's home 
directory there.  End of story.  You can have 200,000
accounts there. 
Doesn't matter.

> Because of filesystem performance it is necessary to
split up the user
> folders.
> Do you know any other way to do this?
> Or are these requirements not true (filesystem
performance)?

Nobody said anything about putting all accounts in a single
parent 
directory.  You can put any account anywhere, as long as you
set its home 
directory in your authentication backend.

Now, one thing that you WILL need to do is have each mail
account have 
something that looks like an ordinary home directory, with a
$HOME/Maildir 
being the actual maildir.  From Courier's perspective, there
is no 
difference whatsoever in holding the account information in
/etc/passwd, an 
LDAP directory, a MySQl db, a Postgres DB, or a a
Courier-specific 
GDBM/DB-based account directory (generated by Perl scripts
from flat files). 

If you use ordinary system accounts, you have your home
directory, your mail 
is in $HOME/Maildir, and that's where you have your mail
server dump it, and 
Courier pick it up.  With Courier, other account
authentication methods -- 
LDAP, MySQL, etc…, are no different.

Account authentication is a black box.  In pops in a login
and a password, 
out pops out the account's home directory (and a uid and gid
that owns files 
beloging to this account). How the login and the password is
validated, and 
how the account's home directory is defined, is abstracted
away.

So you cannot have just a bunch of maildirs splattered all
over the place. 
You need to run a script to take each one of your maildir
mailboxes, and put 
it into its own home directory, naming it
"Maildir".  You can hash all the 
home directories, themselves, in whichever way your heart
pleases, as long 
as you set each account's homedir path in your
authentication database.

You may swap out one authentication module for another, LDAP
→ MySQL → 
PostgreSQL → whatever, as needed, as long as the account
information is 
carefully migrated.

Although it is possible to forego setting up a home
directory for each 
account, and just leave a bunch of naked maildirs all over
the place, I'm 
not going to tell anyone who to do it anymore.  This
inevitably leads to 
problems and headaches in the future, when you'll want to do
something more 
with each account, beyond serving IMAP.  As soon as you do
it, be it 
offering mail filtering, or some other feature, naked
maildirs break down. 
If someone tells you how to do it, and later down the road
you run into 
trouble, go back to them and ask them, not me, what to do.



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On Fri, Mar 09, 2007 at 11:24:11AM +0100, Torsten wrote:
> I want to use a hashing mechanism (nhash) from my MTA
(Exim) to split up 
> the users maildirs into subfolders.
> 
> The directory structure looks like this:
> /var/mail/0/totty or /var/mail/126/bill
> 
> Here is the part from the Exim configuration:
> file =
"/var/mail/${nhash_127:$local_part}/$local_part/INBOX&q
uot;
> 
> My problem is, that I haven`t got a clue how the imap
daemon deals with the
> new directory structure.
> Has courier an implemented hashing mechanism?

No. You'd have to either write an authpipe module which
implements the
authentication plus hashing, or write all the hashed values
into a database.

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I have a simpy idea. Why not split into 26 subfolders (where
you will write 
the maildirs), and the name of subfolder are the 1 letter of
account?

For example:
user:
anibalmyhouse.com ---> /DIR/a/anibal
fredanydomain.com ---> /DIR/f/fred

This give to you the opportunity to split the more large
folders into other 
drive.
/dev/sdc0= --> /
/dev/sdc1= --> /DIR/a

Regards





El Viernes, 9 de Marzo de 2007 23:01, Totty escribió:
> > No.  Courier expects that you will provide each
account's home
> > directory in your authentication database. 
Whatever authentication
> > method you are using - /etc/passwd, LDAP, MySQL,
or whatever, each
> > account must have its home directory defined and
Courier will simply
> > use whatever is set in the account database.
>
> Damned, I couldn`t put the exact home directory to the
database, because
> of Exim (nhash) is calculating the folders.
>
> The reason is that I`m asking for is that I want to
setup a huge server
> with  over 20000 user maildirs.
> Because of filesystem performance it is necessary to
split up the user
> folders.
> Do you know any other way to do this?
> Or are these requirements not true (filesystem
performance)?
>
> Many regards
> Torsten
>
>
>
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On Sat, Mar 10, 2007 at 01:16:49PM -0300, Christian Schmitz
wrote:
> I have a simpy idea. Why not split into 26 subfolders
(where you will write 
> the maildirs), and the name of subfolder are the 1
letter of account?
> 
> For example:
> user:
> anibalmyhouse.com ---> /DIR/a/anibal
> fredanydomain.com ---> /DIR/f/fred

(1) Because it balances very poorly

(2) Because it still doesn't solve the OP's problem (that
is, courier imap
must get its homedir path from some sort of backend
database; it doesn't use
any algorithmic method for mapping a username to a home
directory location)
> 
> This give to you the opportunity to split the more
large folders into other 
> drive.
> /dev/sdc0= --> /
> /dev/sdc1= --> /DIR/a

With a backend database, you can just map some accounts to
/mail1/someuser
and others to /mail2/otheruser arbitarily. Then you can
migrate accounts
between directories easily, e.g. for reasons of balancing
space or disk I/O
load.

Brian.

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