performance/scalability and multiple instances

I am working with someone who has 12 Oracle instances running on a single Sun server. Each of these instances is a data warehouse with anywhere from 50-500 GB of data in it. Each DW is completely unrelated to the others.

They have performance and scalability concerns. My recommendation to them is to split the instances up and put them on separate boxes. They can't buy one server per instance, but at least they could split the 12 instances up over three or four machines.

If they do spread the instances over multiple servers, all servers would share a high-end disk array (Hitachi 9970).

My questions are:

1. Is putting 12 heavy duty, large DW instances on a single box a Bad Idea for performance? It is obviously a Bad Idea from an "all your eggs in one basket" perspective.
2. Is there a white paper or something similar that supports my opinion that scaling unrelated instances horizontally is more scalable than scaling vertically?
3. Other than CPUs, memory, and I/O, are there any other resources that multiple instances on one server contend for? (ie: semaphores, locks, whatever)

They did voice one opinion that might have some merit. They said that if all the instances are running on one large machine, and a few of those instances are idle at the time (instantiated, but not processing any queries), then the remaining databases can take advantage of the unused CPU cycles from the idle instances.

Thanks for any input you might have.

Ron Received on Mon Jan 27 2003 - 14:17:58 CST