[Dovecot] Questiosn about dbox

[Timo Sirainen]

On 24.1.2011, at 15.52, Javier de Miguel Rodrí 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 :)