HP StorageWorks 1000/1500 Modular Smart Array Command Line Interface user guide (347282-004, June 2007)

HP StorageWorks 1000/1500 Modular Smart Array Command Line Interface user guide 45

AStorage overview

Arrays and logical drives

The capacity and performance of a single physical (hard) drive is adequate for home users. However,

business users demand higher storage capacities, higher data transfer rates, and greater protection

against data loss when drives fail.

Connecting extra physical drives (Figure 1) 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.

Figure 1 Multiple physical drives (D1, D2, and D3) in a system

An array controller combines several physical drives into one or more virtual units called logical drives,

which have superior performance, capacity, and/or fault-tolerant features than separate physical drives.

The read/write heads of all included physical drives are active simultaneously, reducing the total time

required for data transfer.

Figure 2 Multiple physical drives (D1, D2, and D3) configured into one 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 physical drives in that logical drive (Figure 3).

Figure 3 Data striping (S1-S4) and data blocks (B1-B12) on multiple physical drives (D1, D2, and D3)

D1 D2 D3

15310

R/W

D1 D2 D3

15311

B11B10 B12

D2D1 D3

15312