Drive Arrays and Fault Tolerance

S1

B1

B2

B3

 

S2

B4

B5

B6

 

S3

B7

B8

B9

 

S4

B10

B11

B12

 

Figure D-3: Data striping (S1-S4) of data blocks B1-B12

For data in the logical drive to be readable, the data block sequence must be the same in every stripe. This sequencing process is performed by the array controller, which sends the data blocks to the drive write heads in the correct order.

A natural consequence of the striping process is that each physical drive in a given logical drive will contain the same amount of data. If one physical drive has a larger capacity than other physical drives in the same logical drive, the extra capacity is wasted because it cannot be used by the logical drive.

The group of physical drives containing the logical drive is called a drive array (or just array). Since all the physical drives in an array are commonly configured into just one logical drive, the term array is also often used as a synonym for logical drive. However, an array can contain several logical drives, each of a different size (refer to Figure D-4).

HP Smart Array 641/642 Controller User Guide

D-3