[ On Monday, June 30, 2003 at 18:24:46 (+0100), Giuliano Gavazzi wrote: ]
> Subject: Re: [Exim] mirror MX
>
> Just to precise what I am aiming at, since the ideas so far seem to
> be centered on the backup side of it. I know I can do backups of the
> primary mailboxes and other, heck, I can actually, and I do, backup
> the mail client folder on my laptop, but this is not the issue. The
> issue is availability.
Then what you need is either of high-availability hardware or possibly
a hot-standby server (or both).
A high-availiability system will keep running even if one or more of its
components fail (mirrored storage controllers and disks, N+1 power
supplies, etc.) and has quick-repair features that don't even require a
shutdown, such as hot-swap network interfaces and disk controllers.
As I explained the the hot-standby server can also take over
transparently and automatically and with very little loss of data if you
arrange to keep it in sync and if you can detect when the primary has
gone offline.
What you have to decide is how much loss of data you're willing to
accept. The answer cannot be "none" -- that's almost impossible to
achieve for all possible disaster scenarios.
You also need to do a proper risk assessment to figure out whether
certain options that reduce risk are worthwhile to employ and which
would be a total waste of your money.
> I want to be able to login onto the secondary
> and get my email (when the primary is unreachable), so this is why
> both secondary and primary must consider the domains local and send a
> copy (with a veeery long retry cutoff) to the other.
No, that's not how you want to do it. You want to use something like
rsync to keep the hot standby machine in sync with the primary. You do
not want to try to send copies of your e-mail to a hot-standby machine.
> So far this
> would be dead easy if it wasn't for the synchronisation issues.
The synchronisation issues are trivial if, and only if, you approach the
problem as I've outlined.
The issue is not really the receiption of e-mail, it's the availablity
and reliability of the IMAP mail store.
--
Greg A. Woods
+1 416 218-0098; <g.a.woods@???>; <woods@???>
Planix, Inc. <woods@???>; VE3TCP; Secrets of the Weird <woods@???>
