HP StorageWorks 1000 Modular Smart Array - Manual (Page 45)

HP StorageWorks 1000/1500 Modular Smart Array Command Line Interface user guide 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.
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)
R/W
D1 D2 D3
15310
L1
R/W
D1 D2 D3
15311
S1
S2
S3
S4
B1
B4
B7
B2
B5
B8
B11 B10 B12
D2 D1 D3
B6
B3
B9
15312