backup mails from alternate storage

[Lars Täuber]

Hi there!

It seems that
# doveadm backup -v backup -fu $MUSER mdbox:"$BKPDIR/$MUSER/mdbox"
doesn't backup all messages stored in alternate storage.

mail_location = mdbox:~/mdbox:ALT=/srv/mail/slow/vmail/%n/mdbox

I don't know how to debug this.
The sizes of the mailboxes in the filesystems of user C are strange:

~/mdbox:
# du -sm
2169

ALT:
# du -sm
25252

backup:
# du -sm
2658

This is with dovecot 2.2.9 on Ubuntu x86_64 14.04.2 LTS.
Is this a bug or am I doing something wrong?

How can I test if messages stored in the alternate storage are successfully backed up?

Thanks
Lars