[Dovecot] Safely restoring backups

[Micah Anderson]

I'm trying to determine what the best way to restore mail with mdbox
is. Restoring using maildir was trivial, I just used rsync
--ignore-existing which wrote any mails that were removed and didn't
touch things that already existed[1]. With mdbox things have become more
complicated, and I haven't found a way to restore mail that doesn't
result in many message duplicates.

My backup setup is simple, I'm doing daily rsync backups of user's
mailstores, as well as weekly backups, so I end up having on my backup
server daily.1, daily.2, daily.3, daily.4, weekly.1, weekly.2... each
containing the entire contents of the user's mdbox.

The different restore methods I've tried are:

1. I tried rsyncing the different backup directories back to the mail
storage host, and then doing:

'dsync -R backup -u $user mdbox:/path/to/to/daily.1/mdbox'[2]
'dsync -R backup -u $user mdbox:/path/to/to/daily.2/mdbox'

This works ok, but it gives duplicates of every mail that already exists
for every daily/weekly I dsync. This is what the rsync --ignore-existing
avoided. This is particularly annoying if I restore the weekly, and
multiple daily directories, because then you get a copy for every one
you restore. I had thought that the individual message's GIDs would keep
them from being duplicated?

2. I also tried to use 'doveadm import' in two different ways. The
first way I created a 'restored_from_backups' folder and then import
each of the daily.#, weekly.# mdboxes into their own subfolder within
that folder, for example:

'doveadm import -u $username mdbox:/path/to/daily.1/mdbox restored_from_backups/daily1 all'
'doveadm import -u $username mdbox:/path/to/daily.2/mdbox restored_from_backups/daily2 all'
... etc.

I then go through and subscribe the new folders[3] and the user ends up
with a folder structure like this:

restored_from_backups/
  daily.1/
        INBOX
        Trash
        folder1
        folder2
  daily.2    
        INBOX
        Trash
        folder1
        folder2
etc.

This works fine, except that it results in the user having a entire
duplicate copies of their mailbox for each daily/weekly that I
restore. That will quickly bring people over quota.

3. I also tried to use 'doveadm import' to import all the different
directories all into the same restored_from_backups directory, so there
are no subdirectories for each daily/weekly under restored_from_backups,
like so:

'doveadm mailbox create -u $user -s restored_from_backups'
'doveadm -v -D import -u $user mdbox:/path/to/daily.1/mdbox restored_from_backups all'

I then go through and subscribe the folders[3].

Using this method, the 'restored_from_backups' mailbox is created, and
populated with the folders. The only problem with this method is the
same as method #1: for every backup I restore, mails are duplicated.

Is there a way I can restore things from backup and avoid duplicates?
Is there another method I should try?

thanks for any ideas, pointers, suggestions for improvement, etc.

micah


1. this would of course bring back mails that were deleted, but that was
fine as the user could deal with that.

2. yes, I know I could setup dsync on the backup server, and use dsync
directly to pull the mails from there, but this is complicated in my
situation due to how the backupserver works.

3. why doesn't doveadm import have a -s option to subscribe? 

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