[Dovecot] The docs a re a bit weird on "Directory hashing"

[Eliezer Croitoru]

In squid we use a double layer of hashed directories on the FS to allow
storage of millions of files.
I was reading the "Directory hashing" section but never understood it..
since it's written.. in a way I could not understand.
I am using this line:
mail_location = maildir:/home/vmail/%d/%n/Maildir/

and I want to migrate to a hash based directory scheme.
While trying to understand how that hash will work I stumbled a old
thread at:
http://www.dovecot.org/list/dovecot/2010-June/049695.html
there they used:
mail_location=maildir:/buzones/us.es/%1Hu/%2.1u/%n

so I assume it should be used like that:
mail_location=maildir:/home/vmail/%H/%2.256Hn/%d_%n/Maildir/
or:
mail_location=maildir:/home/vmail/%1Mu/%2.1Mu/%d_%n/Maildir/

It's a bit hard to think alone so I hope you can assist me.

let say I want to follow the model of squid cache_dir which has:
cache_dir aufs /usr/local/squid/var/cache/squid 40000 16 256

And means a two layers cache of max 16 directories on the first layer
and 256 directories on the second layer.
The above allows millions of files storage and can benefit from all ext4
lower kernel levels of compatibly rather then do stuff on the user-land..
Since I am not 100% sure that the scheme I understood is indeed what I
think I assume the above will need a small correction.

Eliezer