Architecture Advice - Active/Passive Clusters

[SpideySMJ]

I have been asked to consolidate several smaller offices into one main location in our company. Currently, we have three servers setup in our local area, totaling roughly 1900 users. My initial thought was to setup an Active/Passive Exchange Cluster with two servers utilizing our SAN. But during some of my research it's been stated that a single node should not own more than 1900 users. Seeing as how we are already at that number, I'm not comfortable with that configuration. With that in mind, I'm looking at two options:

1) Two separate Active/Passive Clusters, splitting the users up between the two.

2) Or an Active/Active/Passive Cluster with three servers and two Exchange Virtual Server instances.

So finally, here are my questions. Is number 2 viable? Has anyone done a configuration like this before and if so, how many problems did you have? Are there any specific requirements I should be looking at before even suggesting such a configuration?

"I reject your reality and substitute one of my own.

 

[Zelandakh]

Upgrade to Exchange 2007. Have a 2 box mail store set both running continuous cluster replication to each other.

Have a pair of client access servers.

Much better plan.

 

[SpideySMJ]

There is no way that will happen. That changes the scope of the project from 3 local servers to 20 servers across the nation. Adding way more dollars, time, and resources. The solution must stay in Exchange 2003.

"I reject your reality and substitute one of my own.

 

[Zelandakh]

I am prepared to accept some of that but why does that mean 3 Exchange 2003 boxes becomes 20 Exchange 2007 boxes?

You seem to be specifying a cluster which means 3 server, a big SAN with head units and other paraphenalia plus clustering requirements and lots of consultancy bills.

Going Exchange 2007 means 4 pieces of tin, a cheaper SAN or 2 DAS arrays and no clustering headache.

I'd have said it would be cheaper, but you know your company.

Active/Passive. Very difficult to implement fully, but the bugbear comes whenever you want to do something as it can be a house of cards.
Active/Active/Passive means you cannot even used Advanced Edition Windows and you have to go to DataCenter (sic) Edition to get the extra node. There's a full on technet article available and Russ Kaufman did an article on a 2 node cluster and things to think about but I can't find it