Raid 5—distributed data guarding, Information (px,y), 4 raid 1, raid 1+0 features – HP StorageWorks 1510i Modular Smart Array User Manual

Page 148: Figure 6

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Figure 6 RAID 1+0 array, with eight physical hard drives (D1 through D8)

In each mirrored pair, the physical drive that is not busy answering other requests answers any read

request sent to the array. (This behavior is called load balancing.) If a physical drive fails, the remaining

drive in the mirrored pair can still provide all the necessary data. Several drives in the array can fail

without incurring data loss, as long as no two failed drives belong to the same mirrored pair.
RAID 1+0 is useful when high performance and data protection are more important than the cost of

physical drives.

Table 4 RAID 1, RAID 1+0 features

Advantages

Disadvantages

Highest read and write performance of any

fault-tolerant configuration.

Expensive (half of the drives are used for fault

tolerance).

No loss of data as long as no failed drive is mirrored

to another failed drive.

Only half of total drive capacity usable for data

storage.

RAID 5—distributed data guarding

In this method, a block of parity data is calculated for each stripe from the data that is in all other blocks

within that stripe. The blocks of parity data are distributed across every physical drive within the logical

drive (

Figure 7

). When a physical drive fails, data that was on the failed drive can be calculated from the

data on the remaining drives and the parity data. This recovered data is written to the assigned spare or

to a replacement drive in a process called a rebuild.

P5,6

P3,4

P1,2

P7,8

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Figure 7 RAID 5 array, with three physical hard drives (D1, D2, D3) showing

distributed parity information (Px,y)

This configuration is useful when cost, performance, and data availability are equally important.

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Storage overview