HP DL160 HP ProLiant Storage Server User Guide (440584-004, February 2008) - Page 53

• Include the appropriate number of physical drives in the arrays to create logical storage elements of desired sizes. Arrays See Figure 16. With an array controller installed in the system, the capacity of several physical drives (P1-P3) can be logically combined into one or more logical units (L1) called arrays. When this is done, the read/write heads of all the constituent physical drives are active simultaneously, dramatically reducing the overall time required for data transfer. NOTE: Depending on the storage server model, array configuration may not be possible or necessary. L1 P1 P2 P3 gl0042 Figure 16 Configuring arrays from physical drives Because the read/write heads are simultaneously active, 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 17. S1 B1 B2 B3 S2 B4 B5 B6 S3 B7 B8 B9 S4 B10 B11 B12 gl0043 Figure 17 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 contains 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. HP ProLiant Storage Server 53