Multi-dbox storage space

[MRob]

On 2019-02-03 21:12, Philon wrote:
>> 
>> On 03 Feb 2019, at 22:07, MRob <mrobti at insiberia.net> wrote:
>> 
>> Hi, I originally picked mdbox because I had the impression from 
>> reading about it on the mailing list that it was more performant and 
>> that it would conserve disc space.
>> 
>> But lately i found mailboxes have nearly double the storage as 
>> reported. I mean, IMAP QUOTA reports around 900MB for one account that 
>> has over 2GB when I inspect the mail location of the user using the 
>> linux command `du`
>> 
>> Another account has around 750MB according to IMAP but using du I find 
>> 1.5GB. This is for message files and index files combined.
>> 
>> Is this normal? I tried to read the MailboxFormat/dbox wiki page and 
>> it does not directly address this topic but it does reference "doveadm 
>> purge". Do I need to use "doveadm purge"?
> 
> From https://wiki2.dovecot.org/MailboxFormat/dbox:
> 
>> Expunging a message only decreases the message's refcount. The space 
>> is later freed in "purge" step.

Thats what I read but I had a hard time to believe I could understand it 
was a critical maintenance because it was not highlighted in the docs.

I ran purge and find now "du" reporting about 60% the size of IMAP QUOTA 
so mdbox now is saving space and I'm very happy for Dovecot again is 
good software. But may I ask developers it is not common belief of 
administrators to know they must purge message storage - can you please 
make this a warning in highlight and big text on the mailformat 
documentation? I think this is a ciritcal oversight

PS for 10.000+ users how heavy is this process on performance? what if 
100.000+ users?