Replication and backups

[Patrick Goetz]

Hi -

I'm grappling with the issue of how to either do backups or take 
snapshots of a live cyrus system so that all the metadata is properly 
saved; meaning that the indexes and db files match exactly the messages 
in ~/cyrus/mail so that the backup or snapshot can be copied to a new 
system and brought up cleanly when cyrus is started.

I recall someone on this list mentioning that they use LVM snapshots for 
this purpose, but I did a little research on this, and it appears that 
file system performance degrades dramatically when LVM snapshots are used.

What I'm thinking about using instead is replication with DRBD to 
another server, turning off the replication periodically, making a 
backup of the replicated filesystem, and then turning replication back 
on.  Even here, though, it seems like it would be possible turn off the 
replication after a new message has been stored but before either the 
indexes or the .db files are updated.

Is there any way to get around this or has the application been coded to 
be "transaction safe"?  This is one advantage of maildir format:  the 
metadata is just built right into the message filename, so the only 
thing that can get lost or corrupted is the indexes, which can just be 
rebuilt.  Of course there's a sizable performance penalty that comes 
with this...