[CentOS] postfix mail server
vogelke+centos at pobox.com
Tue Sep 18 02:25:50 UTC 2012
>> On Mon, 17 Sep 2012 20:57:25 +0200,
>> Reindl Harald <h.reindl at thelounge.net> said:
R> point 3 [Backup must be easy] is bullshit. have fun tar/rsync
R> maildir/mbox CONSISTENT while the server is up. nothing easier than
R> that with database-replication.
Backing up maildirs doesn't require any downtime because a maildir is
atomic in every way that matters. It uses filename and location to
indicate message status. If you want to back up *live* Maildir folders,
either one of these will do:
Unless your users are in the habit of editing messages, Maildir files
don't get modified; they're created, renamed and deleted. When users do
edit messages, the mail client normally creates a new one and deletes
the old one. As a result, rsync isn't the most efficient way to sync
maildirs -- when status changes occur, rsync sees that a new file exists
and an old one is gone. It doesn't know that the file was renamed.
The only real issue when backing up a Maildir using tar/rsync is speed.
Neither method is great when backing up a large number of small files, as
many people have observed in the past. Common workarounds:
* using dump/restore (requires a quiescent filesystem), or
* using tar/scp for the first Maildir backup and using rsync afterwards.
All you need for this case is an SMTP server that understands Maildirs.
Contrast this with an RDB, where you absolutely need consistent and quiet
files to do a successful backup. If you want DB replication, then you need:
* an SMTP server, plus
* an RDB on the mailserver, plus
* a replica of the DB on another server.
Which setup is easier to create and maintain?
Karl Vogel I don't speak for the USAF or my company
She made me a mix tape called "Sorry I Barfed On Your Comforter".
--Jimmy Fallon, #thatsmyroommate tweets, 14 Sep 2012
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