HP StorageWorks 4000s NAS 4000s and 9000s Administration Guide - Page 54

Storage Management Overview L1 P1 P2 P3 Figure 25: Configuring the physical drives into an array dramatically improves read/write efficiency 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 termed a block. The blocks form a set of data stripes over all the hard drives in an array, as shown in Figure 26. S1 B1 B2 B3 S2 B4 B5 B6 S3 B7 B8 B9 S4 B10 B11 B12 Figure 26: RAID 0 (data striping) (S1-S4) of data blocks (B1-B12) For data in the array to be readable, the data block sequence within each stripe must be the same. 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 hard drive in a given array will contain the same number of data blocks. Note: If one hard drive has a larger capacity than other hard drives in the same array, the extra capacity is wasted because it cannot be used by the array. 54 NAS 4000s and 9000s Administration Guide