Backup vs replication

[ellie timoney]

Hi Albert,

The main logical difference between ordinary replication and the experimental backup system in Cyrus 3.0 is that in a replicated system, the replica is a copy of the account's current state (as of the last replication).  The backup system is a historical record, not just a current state (with configurable expiry period for deleted content).

The main storage difference is that the backup system is two-files-per-user, whereas replication with normal mailboxes is one-file-per-message.  So the backup system has radically lower inode usage, and the gzip compression can benefit from seeing the entire user contents (depending on your users' usage patterns).

The backup system is mainly intended for organisations who keep their backups on online HDD storage, and who want to condense backups for a relatively large number of mail servers down to a relatively small number of backup servers (hence the massive inode reduction).  If you plan to use tape or other offline storage for backups, just use a normal replica so you can stop cyrus during backups without causing downtime, and dump its filesystem(s) to tape.

The backup system is also experimental.  Please do not use it as your sole backup mechanism.

Cheers,

ellie

On Sat, May 19, 2018, at 6:46 AM, Albert Shih wrote:
> Hi everyone,
> 
> I'm not sure I really understand what's the benefice of backup (cyrus>3.x) vs
> replication ?
> 
> Is the main goal are to save disk space with compression ? Less inode (with
> large file) ?
> 
> I believe the add backup feature to cyrus-imapd was/still very lots of
> work. So what's the advantage of backup vs replication_over_compress_fs.
> 
> Regards
> --
> Albert SHIH
> DIO bâtiment 15
> Observatoire de Paris
> xmpp: jas at obspm.fr
> Heure local/Local time:
> Fri May 18 22:42:34 CEST 2018
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