Formation of a RAID array Understanding RAID arrays can be difficult due to the complex disk arraignments and disk geometries involved. In addition, the naming convention is not very user friendly either. Common to every arraignment and geometry is a lower level hierarchy in which data in a RAID system is organized: 1. Physical Drives: The physical, actual hard disks that comprise the array are the "building blocks" of all data storage under RAID. 2. Physical Arrays: One or more physical drives are collected together to form a physical array. Most simple RAID setups use just one physical array, but some complex ones can have two or more physical arrays. 3. Logical Arrays: Logical arrays are formed by splitting or combining physical arrays. Typically, one logical array corresponds to one physical array. However, it is possible to set up a logical array that includes multiple physical arrays. 4. Logical Drives: One or more logical drives are formed from one logical array These appear to the operating system as if they were regular disk volumes and are treated accordingly but the RAID controller is transparently managing the actual hardware.
Most RAID setups consist of a number of physical drives made into a physical array, which is made into a logical array, which is then made into a logical drive. This array hierarchy and management are "hidden" from the operating system. | 
