[Dovecot] Deduplication active - but how good does it perform?

[Charles Marcus]

On 2012-01-06 6:58 AM, Charles Marcus <CMarcus at Media-Brokers.com> wrote:
> On 2012-01-06 5:54 AM, Timo Sirainen <tss at iki.fi> wrote:
>> On 6.1.2012, at 12.09, Ralf Hildebrandt wrote:
>>> I have deduplication active in my first mdbox: type mailbox, but how
>>> do I find out how well the deduplication works? Is there a way of
>>> finding out how much disk space I saved (if I saved some :) )?
>
>> You could look at the files in the attachments directory, and see how
>> many links they have. Each file has 2 initially. Each additional link
>> has saved you<size of file> bytes of space.
>
> Maybe there could be a doveadm command for this?

Incidentally, I use rsnapshot (which is simply a wrapper script for 
rsync) for my disk based backups. It uses hard links so that you can 
have hourly/daily/weekly/monthly (or whatever naming scheme you want) 
snapshots of your backups, but each snapshot simply contains hardlinks 
to the previous snapshots, so you can literally have hundreds of 
snapshots that only consume a little more space that one single whole 
snapshot.

Anyway, rsnapshot has to leverage the du command to determine the amount 
of disk space each snapshot uses (when considered as a 
separate/standalone snapshot), or how much *actual* space each snapshot 
consumes (ie, only the files that are *not* hardlinked against a 
previous backup)...

Maybe this could be a starting point for how to do this...

http://rsnapshot.org/rsnapshot.html#usage

and scroll down to the rsnapshot du command...

-- 

Best regards,

Charles