Robert Hercz wrote:
> ChrisP,
>
> We're also in the process of setting up mirrored
servers and this confuses
> me somewhat:
>
> I thought we could achieve maximum uptime by having two
servers on two
> different public IP address (from two different network
providers), and have
> the MX record in our DNSs use one as a primary (higher
number) and the other
> as a secondary server.
Yes you can do that.
>
> This would mean that both will receive e-mail, and
whenever we need to take
> a server down for whatever reason, the other would
send/receive as if
> nothing happened.
Correct. This is a reasonable setup. But your users would
still need to
manually choose the backup server if the primary was down,
as mx records
don't work for pop/imap...
>
> Can you please elaborate on what messy situations we
could run into if
> mirroring should fail, and in which circumstances
mirroring actually could
> fail?
Ok, now I try and come up with an actual scenario I can't
actually think
of anything that would induce a serious problem. Lets just
say I'm
paranoid enough to believe there may be some situation where
it might
occur even if I can't think of one. I have a general belief
that
complexity decreases reliability and if your configuration
uses both
systems 'normall'y then if either system partially fails
(e..g. a full
disk) the users will notice until such time as you turn off
the faulty
system.
I believe it's best to 'manually' fail over to the slave so
that you are
always 100% sure which machine has all the up to date data.
Here's the worst thing I can think of, your mirror server
looses it's
link to the master, but keeps receiving external email, then
a day later
it blows up and the disk fails. In this situation you've
lost a days
worth of email that got delivered to the mirror.
Using a monitor process to check that the mirroring is
working and 'in
sync' every hour would hugely reduce any such risk, most
issues would
only get serious if the mirroring was blocked (e.g. by a
firewall
change) and then some other catastrophe occurred before the
network
issue is resolved and the sync can catch up.
So by all means do it the way you describe above, that is
quite a
reasonable approach.
>
> Rgds,
> Robert H.
>
> -----Opprinnelig melding-----
> Fra: SurgeMail Support [mailto:surgemail-support netwinsite.com]
> Sendt: 25. mars 2008 22:37
> Til: surgemail-listnetwinsite.com
> Emne: Re: [SurgeMail List] Mirrored servers
>
> Mark Jones wrote:
>> We are in the process of setting up 2 servers that
will be mirrored.
>>
>> I want to get clarafication on how we should be
using them. Should we
>> limit traffic to only one of the servers and use
the other as a hot
>> standby or can we direct traffic to both. When I
say traffic I mean
>> ingoing and outgoing smtp as well as webmail.
>>
>> Thanx
>>
>
> Hi,
>
> We recommend you direct traffic to only one, that way
the other is
> simply a hot standby and if the mirroring fails, then
nothing bad
> happens. If you run the traffic to both, and the
mirroring fails then
> you have a 'mess' to untangle that
> may be very ugly.
>
> But you 'can' send or receive email on both if you
wish, it just adds a
> slight 'risk' which I personally don't like.
>
> ChrisP
>
>
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