[Dovecot] 76Gb to 146Gb

[Stan Hoeppner]

On 9/25/2012 12:29 AM, Spyros Tsiolis wrote:

> My clients don't invest in hardware. I live in Greece. Things are really
> bad right now. Not that if they were better they (the client) would invest
> in their infrastructure.
...
> Thank you very much Stan for you kind reply.
> 
> I reply to you in private since I was told to stop the thread
> on the dovecot list because it's off-topic.

I'm going to bring it back on topic.  To recap the issue:

1.  73GB volume, ~82% full.  Volume contains OS, spool, and mailboxes
2.  Two 146GB drives on hand that are impossible to employ in either
    a live or offline migration due to hardware limitations--drive slots

(0.82*73GB=60GB)-5GB(OS)= ~55GB/40= ~1.375GB/user mailbox

(This math assumes the box has already been scoured and things like
source files and other temporary stuff has already been removed, along
with anything and everything not necessary to the primary functions of
this box)

1.375GB/user suggests these users seem to horde old emails, or simply
don't keep their mailboxes tidy.  Normally I'd guess that a lot of space
in a situation like this is taken up by full text search indexes, but
you don't appear to have these enabled.

I notice in your 'dovecot -n' output that you are already employing
zlib, but to what degree is currently unknown to the list.  Are you
compressing maildirs with a nightly script?  If not, and you're
compressing on an ad hoc basis, realtime compression during write could
save you quite a bit of additional space, extending the operating life
of your current drives.  Of course a simple request to your users to
clean up their mailboxes would surely help as well, if that's a
possibility--some users would flog one for making such a suggestion.

If you're not fully taking advantage of compression currently, you may
want to consider upgrading to Dovecot 2.x which allows transparent
compression to dbox and maildir storage.  You may want to migrate to
mdbox message store format while still using zlib, and enable single
instance attachment storage (SIS).  As the name suggests, SIS saves an
attachment only once, regardless how many user emails in which it
exists.  See:

http://wiki2.dovecot.org/Plugins/Zlib

I'd point you to the docs for SIS but I'm unable to find them in the
Wiki.  Surely someone else can provide the settings and/or update the wiki.

-- 
Stan