Connecting extra physical drives (Pn in the figure) to a system increases the total storage capacity but has no effect on the efficiency of read/write (R/W) operations. Data can still be transferred to only one physical drive at a time.

With an array controller installed in the system, the capacity of several physical drives can be combined into one or more virtual units called logical drives (also called logical volumes and denoted by Ln in the figures in this section). Then, the read/write heads of all the constituent physical drives are active simultaneously, reducing the total time required for data transfer.

Troubleshooting 117