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Re: realtime email backup across computer centers

On Tue, 2003-05-13 at 10:39, Stephan Poehlsen wrote:
> Hi,
> How would you realize a realtime email-backup across two different
> computers in two different computer-centers?
> Let's say I have a mail-server A in city A and a backup-mail-server B
> in city B. So if an airplain crashs one computer-center, no email gets
> lost.
> I think all mail must be forwarded from server A to B (and must be
> acknowledged from B) before server A acknowleges incomming mail.

You could use DRBD to have your spool-directory mirrored. If machine A
goes down, B mounts the DRBD device and takes over the IP address of
your mail-service. Voila, you're up again. Downtime: a few seconds...

The only real problem I see:  If you really want to distribute your
servers across two cities (!), you'll need some really good (i.e.
stable) connection between both servers or you may face a split-brain
situation. A fast Uplink may be nice to as you have to re-sync your
whole device every time one of your servers go down.
Typically DRBD has some Gbit interconnect through a crossover cable to
prevent such a situation due to a switch-failure or something else and
provide reasonable fast re-sync times.

> Does there exists a solution? Maybe with qmail?

The scenario above is completely MTA independent - you can use qmail,
sendmail, postfix, exim, courier-mta, $whatever... 

best regards,
Markus Oswald <moswald@iirc.at>  \ Unix and Network Administration
Graz, AUSTRIA                     \ High Availability / Cluster
Mobile: +43 676 6485415            \ System Consulting
Fax:    +43 316 428896              \ Web Development

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