Re: Active/Active Clustering
From: Russ Kaufmann [MCT] (russ_at_exchangemct.nospam.com)
Date: 07/20/04
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Date: Tue, 20 Jul 2004 14:50:13 -0600
"John Toner [MVP]" <jtoner@mvps.DIE.SPAM.DIE.org> wrote in message
news:eJjjfipbEHA.3752@TK2MSFTNGP12.phx.gbl...
> Just to add my $0.02...I am a big fan of A/A clustering...as long as you
are
> not going A/A with a single application (like Exchange).
Or SQL, or SQL on one node ane Exchange on another. <G>
> I've had lots of
> success with Active/Active clustering...big Exchange/SQL server on one
node
> and file & print on the other node.
That is a pretty reasonable way to go so long as the servers are sized
correctly. However, I believe the original post was about databases. So, an
active/passive would probably be best in most cases.
> I have also have had very little success
> with Active/Active applications in a cluster.
Yep, we all agree this is not a good scenario.
> In my experience, its a much
> easier "sell" if you do not have idle hardware. If you plan appropriately,
> never utilizing more than 50% of the resources on a server, you can
achieve
> A/A clusters with great success rates.
>
> The problem that usually occurs in this situation is that applications
tend
> to grow and servers quickly use up more resources then they're originally
> planned to utilize. Since you see no immediate degradation of your
> applications, it's easy to forget that its part of a cluster and that it
> WILL eventually host all applications on the single server. When this
> happens, that where you'll usually have issues. This can be avoided with
> careful monitoring of your servers peak utilization statistics.
The problem, and reason why I really push towards A/P is that in an A/A, the
apps grow and even if an admin watches it closely, he/she may not be the
admin during the entire lifetime of the A/A cluster. A mistake that many of
us make is that we build for ourselves and our skills and not the skills of
others that may inherit our systems.
> If you've got the budget, you might want to stick to an Active/Passive
> cluster, but once you start looking at bigger clusters, it starts making
> less sense to stick with an Active/Passive model. If you've got an 4-node
> cluster, this means that you're going to have half of the servers sitting
> "idle" waiting for one of the other two to die.
Why would you necessarily do that when you can go A/A/A/P?
> In my opinion, this is
> overkill as it would be pretty rare to have 2 servers die simultaneously
> (though possible of course). If it's an 8-node cluster, the idle time gets
> more expensive in the 1:1 A/P model. I'd have no problem recommending a 6
> Active, 2 Passive model to customers or even a 7:1 split in 8 node
cluster.
Absolutely! Configuring a bunch of A/P clusters makes no sense if you can
configure an A/A/A/A/A/A/P/P or A/A/A/A/A/A/A/P monster that takes full
advantage of the resources and still allows for smooth failover.
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