1) I am not familiar with the U320 adapter, but when you power on the server it goes throught the POST (power-on selft test). As part of this it initializes all adapters. Some of them give you a message which key combination (e.g. CONTROL+C, ALT+Q) to press and a few seconds to act. Once you have pressed this keys, the adapter's maintanance program is entered - I'm sure you have seen such messages already like pressing [F8] to configure the iLO.
2) Well, many operating systems (Linux, Windows) offer a so-called host-based RAID. On Linux this is the 'md' driver, on Windows you use 'fault tolerant sets'. The advantage of the SmartArray controller is, that it 'hides' the individual disks from the operating system and automates some tasks like handling a spare disk while you often have to do more work on the operating system
e.g.: you can only boot from a physical disk drive. The operating system can mirror that data, but what happens when the physical boot member dies and the operating system goes down? You have some work to get the system boot from the mirror. A SmartArray controller hide this nicely, because it always presents a single 'pseudo disk' that appears to work fine unless you have multiple disk failures.
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