I have a server with 3 hard drives installed, and a total capacity of 6. We're planning to max it out, but our consultant also suggested getting a second RAID controller "for redundancy" to support the new drives. To me, this doesn't make much sense. Even with a second RAID controller running half of the disks, we're still stuck with only half of our disks/programs/data if one of the controllers dies (which isn't much better than running with none). We're putting vmware on the server and he vaguely mentioned some advanced fault tolerance/failover features, but if the disks are inaccessable due to a failed controller, how is it supposed to work?
Counting only reasons for redundancy, not performance, why would I want to have a second RAID controller in my server?
Best Answer
In a 'single box high availability' design then yes, you'd want a second controller, ideally on a second bus too. But this kind of approach has given way to a cheaper design based around clustering where one box failure doesn't stop service. So it depends on if you plan to use a clustered environment or rely on a single box. Even if your answer is the latter having dual controllers may be seen as adding extra complexity and maybe being overkill.
edit - based on your comment about using ESXi on your other question I'd have to say that its clustering is fabulous, we have many 32-way clusters that work brilliantly.