To address the issues of other reviews, yes the rebuilds take a while but this is true of other controllers at this pricepoint such as Adaptec's 5805 card which costs a couple hundred dollars more. The arrays are available while rebuilding a mirrored volume so yes, there's a performance hit during the rebuild but at least your boot/data volumes are available during this process.
I tested out the failover mode by pulling out a drive while the system was online from a mirrored volume set. I don't recommend doing this as this controller is NOT hot swappable but it recovered fine and the volume was in a critical but useable state. This card is good if it's important to keep your system online 24x7. If you're looking for performance, get a high speed SAS RAID controller and some external drive towers.