It means
Disk Array Controller or
RAID Controller often improperly shortened to a
Disk Controllers. It is a device which manages the physical disk drives and presents them to the computer as logical units. It is used to implement hardware RAID.
Redundant Array of Independent Disks (RAID) is a storage technology that combines multiple disk drive components into a logical unit.
For further reference:
Disk Array Controller &
RAID
So to answer your question, I guess 2 disks are connected to 2 different RAID Controllers not one.