[Dovecot] Some questions about mdbox

[Maria Arrea]

Hello

 I am starting testing with dovecot 2.0.9. In my  //etc/dovecot/dovecot.conf/ I have the following line:


 /mail_location = mdbox:/mydomain.org/%2.26Hn/%2.200Hn/%n:INDEX=/mydomain.org/indexes/%2.26Hn/%2.200Hn/%n/


 These are my questions (a long mail):

 *1º How should I restore from backup with mdbox & separate indexes?*

 I have read in dovecot list archive about restoring the full user mailbox to a temp location and then run something like:

 /doveadm import mdbox:/tmp/restored_mailbox/ "" savedsince 2011-01-01 / In my schema indexes and mail stores are in separated paths. What (and where!) should I copy to the temp location and how do I restore it?

 *2º Disaster recovery: indexes & mail store mismatch*

 When creating backups, indexes and mail store are in different paths. My backup takes several hours, so indexes are copied BEFORE mail stores. Is the backup consistent?

 What would happens if I lose indexes? Can I still recover the messages? Reading the doc it seems I would lose all the message flags and all the messages would be in INBOX, is this right?

 *3º Performance tuning with mdbox*

 I have read in dovecot archive about using mdbox_rotate_size & mdbox_rotate_interval to balance between a lot of smaill files (like Maildir) or really big files (a "variant" of mbox). I have tested with a big vaule of mdbox_rotate_size (100 MB) and is a complete disaster for backup:if a user delete a message, then a nightly cronjob purges the mailbox (refcount=0) a new mdbox .m file is created!. So deleting a 1 k message from the mailbox of an user is a new 99 MB file to backup. Any hint about this?

 I am also using ext4 (rw,noatime,nodiratime,commit=15,data=writeback) and I have read about mdbox_preallocate_space. I will try it, any hint about this setup? This is not still in production, so I have no idea about IOPs and user concurrency, but I have several thousand users.


 *4º Compression with mdbox*


I am reading about compression in mdbox (zlib/bzlib). I am starting with zlib, has anyone experience with bzlib? How much load is bzlib against zlib and how much delay adds to user experience (and space savings vs zlib???) ?


 *5º Recover a message with refcount=0*

 Is there any way to recover a message with refcount=0 without using a backup? I am thinking about the following plan:

 /1º a user gets her mail via pop3 (or delete a message via imap and empties trash)
 2º the message is still stored in my mail server, but has refcount=0
 3º nightly backup is performed
 4º nightly cronjob purges the mailbox (deleting messaged with refcount=0)/


 Using this schema the backup is bigger, but If I can recover files with refcount=0 from backup we can give our users a safeguard against accidentaly deleted pop3 mail.


 Thank you very much for your responsed and sorry for my (awful) english!

 Maria