Hp StorageWorks 1510i Modular Smart Array Manuale Utente Scaricare il pdf (Pagina 86)

B11B10 B12

D2D1 D3

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Figure 17 Data striping (S1-S4) and data blocks (B1-B12) on multiple physical drives

(D1, D2, D3)

For data in the logical drive to be readable, the data block sequence must be the same in every stripe.

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 physical drive in a given logical drive will

contain the same amount of usable space. If one physical drive has a larger capacity than other

physical drives in the same logical drive, the extra capacity is wasted, because it cannot be used by

the logical drive.

The group of physical drives containing the logical drive is called a drive array (or just array). Because all

physical drives in an array are commonly conﬁgured into just one logical drive, the term array is also

often used as a synonym for logical drive. However, an array can contain several logical drives, each of

adifferentsize(Figure 18).

D1 D2 D3 D4 D5

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Figure 18 Two arrays (A1, A2) containing ﬁve logical drives (L1 through L5) spread

across ﬁve physical drives (D1 through D5)

Each logical drive in an array is distributed across all of the physical drives within the array. A logical

drive can also extend across more than one storage enclosure attached to the array system.

Drive failure, although rare, is potentially catastrophic. For example, in Figure 18, failure of any one

physical drive in an array causes every logical drive in the array to suffer irretrievable data loss.

To protect against data loss due to physical drive failure, logical drives are usually conﬁgured with fault

tolerance.

Fault-tolerance levels

To protect against data loss due to physical drive failure, logical drives are usually conﬁgured with fault

tolerance. The following conﬁguration types are available:

•RAID0—nofaulttolerance

• RAID 1+0—drive mirroring

• RAID 5—distributed data guarding

• RAID 6—advanced data guarding

For any conﬁguration except RAID 0, further protection against data loss can be achieved by assigning a

drive as an online spare. This drive contains no data and is connected to the same controller as the

array. When any other physical drive in the array fails, the controller automatically rebuilds information

86 Storage overview

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Hp StorageWorks 1510i Modular Smart Array Manuale Utente Pagina 86