Re: [exim] [Off topic] Replicated mail storage system - unis…

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Author: Renaud Allard
Date:  
To: Marc Perkel, renaud
CC: exim-users, Nigel Metheringham
Subject: Re: [exim] [Off topic] Replicated mail storage system - unison
On Tue, 28 Apr 2009 07:21:25 -0700 Marc Perkel <marc@???> wrote

> Renaud Allard wrote:


> >
> > I used to have this kind of system working using unison
> > (http://www.cis.upenn.edu/~bcpierce/unison/) for the two way replication.
> > Assuming the messages don't change once they are written to disk, you can
> > configure unison with a good performance. I would suggest you to take the
> > latest
> > development version of unison as it has some improvements on how conflicts
> > can
> > be solved if they occur.
> > You will of course need to use a Maildir storage for this to work.
> >
> >
> >
>
> That unison looks interesting. I'm just wondering - is it better than
> just running rsync if you just want to get a backup of maildir
> directories every hour or so?


If you only want a backup, rsync will work just fine. Unison allows for 2 ways
replication, so if a file is created on any of the nodes, it is replicated to
the other. If a file is deleted on any of the nodes, it is deleted on the other.
This is something rsync can't do by itself.
Another advantage of unison is that you can tell it to not check for
modifications of files (typically mails, as they are not supposed to change once
they are created). This may reduce load in some circumstances.