HP StorageWorks Modular Smart Array 1000 HP StorageWorks 1000/1500 Modular Sma - Page 45

A Storage 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. R/W D1 D2 D3 15310 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. R/W L1 D1 D2 D3 15311 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). S1 B1 B2 S2 B4 B5 S3 B7 B8 S4 B10 B11 D1 D2 B3 B6 B9 B12 D3 15312 Figure 3 Data striping (S1-S4) and data blocks (B1-B12) on multiple physical drives (D1, D2, and D3) HP StorageWorks 1000/1500 Modular Smart Array Command Line Interface user guide 45