Drive Arrays and Fault Tolerance

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). Then, the read/write heads of all the constituent physical drives are active simultaneously, reducing the total time required for data transfer.

L1

P1

P2

P3

Figure D-2: Physical drives configured into a logical drive (L1)

Because the read/write heads are active simultaneously, the same amount of data is written to each drive during any given time interval. Each unit of data is called a block, and adjacent blocks form a set of data stripes across all the physical drives that comprise the logical drive (refer to Figure D-3).

D-2

HP Smart Array 641/642 Controller User Guide