dovecot - Jan 2011 - Questiosn about dbox

Hello

     I have read carefully about dbox 
(/http://wiki2.dovecot.org/MailboxFormat/dbox/) and I have some questions:

     - One of the main advantages (speed wise) of dbox over maildir is 
that index files are the only storage for message flags and keywords. 
What happens when we want to recover some messages from backup? With 
maildir we can rebuild message indexes, but I am not sure about dbox. 
Should we also restore "old indexes" and  merge with the "new
indexes"
in order to restore the deleted messages?


     - The previous question applies to sdbox and mdbox. In the case of 
mdbox, we can configure rotation of files using /mdbox_rotate_size/ . We 
would like to rotate daily, not based in size (our users ask us for 
yesterday's backup). How can we accomplish this?


     We have now 17.000.000 messages in our maildir, almost 1.5 TB (zlib 
compresssion enabled). Our backup time with bacula is rather bad: 24 
hours for a full backup, most of the time the backup is busy fstat'ing 
all those little messages. We think that mdbox can help us in this. Does 
anybody has good experiences migrating from maildir->mdox in
"large"
enviroments? What about mdox performance & reliability?

     Thank you for your support

     Javier

On 24.1.2011, at 15.52, Javier de Miguel Rodr? guez wrote:
>    - One of the main advantages (speed wise) of dbox over maildir is that
index files are the only storage for message flags and keywords. What happens
when we want to recover some messages from backup? With maildir we can rebuild
message indexes, but I am not sure about dbox. Should we also restore "old
indexes" and  merge with the "new indexes" in order to restore
the deleted messages?
The intended way to restore stuff is to either restore the entire dbox to a temp
directory, or at least all the important parts of it (indexes + the files that
contain the wanted mails) and then use something like:

doveadm import sdbox:/tmp/restoredbox "" savedsince 2011-01-01
>    - The previous question applies to sdbox and mdbox. In the case of
mdbox, we can configure rotation of files using /mdbox_rotate_size/ . We would
like to rotate daily, not based in size (our users ask us for yesterday's
backup). How can we accomplish this?
mdbox_rotate_interval = 1d

But note that that doesn't guarantee that there will be only one file. Even
if you set mdbox_rotate_size to 10 GB or something (or I think 0 makes it
unlimited, not sure), it's possible that two files will be created if mails
are being saved at the same time. mdbox never waits for locks when writing to a
file, instead it'll just use another file or create a new one.

Anyway, if it's not a big deal restoring the user's entire mailbox
temporarily you can restore only yesterday's mails by giving proper search
query parameter to doveadm import.
>    We have now 17.000.000 messages in our maildir, almost 1.5 TB (zlib
compresssion enabled). Our backup time with bacula is rather bad: 24 hours for a
full backup, most of the time the backup is busy fstat'ing all those little
messages.
In case of Maildir there's no point in fstating any mail files. I'd
guess it should be possible to patch bacula to not do that.
> We think that mdbox can help us in this. Does anybody has good experiences
migrating from maildir->mdox in "large" enviroments? What about
mdox performance & reliability?
I haven't recently heard of corruption complaints about mdbox.. Previously
when there were those, I didn't hear of complains about losing mails or
anything, so that's good :)