Essentially if you have two servers and want to leverage the most out of them you would use an active/active (if one fails the instance fails over to the second node and vice versa). Obviously this is good when everything is fine cause you get two servers, double the grunt and can share databases between the two.

Essentially what you will have are two active/pasive clusters (that fail to each other).

The situation gets better if you can have a third node which can be a shared passive notde for the two active nodes. BUT and heres the disadvantages: If you have a shared passive for both active nodes, what happens if they both failover to the passive? Can it handle the load? Remember to be part of a Windows cluster the hardware must be identicle, so following failover your active instances will be sharing 1 node so will have less the 50% of the resources they had.

We are in a fortunate position where investment for infrastructure has never been an issue. We have two active/passive clusters (2 seperate nodes per cluster) and a thrid node (per cluster) at SCF for database mirror failover.

Back to your questions: As i see it the disavantages with a/a are that it is not a high availability solutiion r ather a high performance solution. What happens in the case of a failure? What is acceptable to the business? Only you or your boss can answer these questions.

For my money, i'd rather have half the grunt but now i am protected! A/P all the way.

Hope this helps.