HP StorageWorks MSA1510i HP Storage Management Utility user guide (383075-002, - Page 85

A Storage overview, Arrays and logical drives

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A Storage overview • Arrays and logical drives • Fault-tolerance levels • Comparison of RAID Methods • Choosing a RAID level 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 a hard drive fails. Connecting extra physical drives to a system increases the total storage capacity (Figure 15), but has no effect on the efficiency of read/write operations. Data is still transferred to only one physical drive at a time. R/W D1 D2 D3 15310 Figure 15 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 16 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 17). HP Storage Management Utility user guide 85

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A Storage overview
•
Arrays and logical drives
•
Fault-tolerance levels
•
Comparison of RAID Methods
•
Choosing a RAID level
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 a hard drive fails.
Connecting extra physical drives to a system increases the total storage capacity (
Figure 15
), but has
no effect on the ef
fi
ciency of read/write operations. Data is still transferred to only one physical drive
at a time.
R/W
D1
D2
D3
15310
Figure 15 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.
L1
R/W
D1
D2
D3
15311
Figure 16 Multiple physical drives (D1, D2, and D3) con
fi
gured 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 17
).
HP Storage Management Utility user guide
85