Does anyone happen to know what all the physical differences are between a single controller and a dual controller? Is there a way to tell from a part number on an invoice if it should have single or dual?
The controllers on the SAN are the connection of the servers to the storage. Multiple controllers allow for multipathing and failover.
I believe the NetApp 2020 is a fiber only SAN (might be wrong, never followed the NetApp gear a lot). So, to set it up correctly with the multipath and failover requires at least 2 good fiber switches and the architecture designed correctly (you are setting this all up correctly, right?)
As it seems, from your question, that you aren't too familiar with SAN's and the technology, I would probably recommend hiring out a good, knowledgeable consultant to help you with setup and some training.. but that's really only part of it. Administration/Maintaining and running a SAN can be a complex thing and many companies have dedicated SAN people depending on the size of their environment.
If you aren't that familiar with the whole SAN world, in particular fiber, I would probably recommend a good iSCSI SAN along the lines of the EqualLogic devices.
I ama system engineer, mostly for HP. I ordered for a customer what was supposed to be a dual controller fas2020. They set it up, and has no second controller. My NetApp knowledge is very limited. my distributor somehow changed the config to a single without informing me of the change.