Raid 5-Distributed Data Guarding; Raid 1+0 Array, With Eight Physical Hard Drives (D1 Through D8); Raid 1, Raid 1+0 Features - HP StorageWorks 1510i - Modular Smart Array User Manual

S1 B1
S2
B5
D1
D5
S1
B1
S2
B5
Figure 20 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
Highest read and write performance of any
fault-tolerant configuration.
No loss of data as long as no failed drive is mirrored
to another failed drive.
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 21). 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.
S1
B1
S2
B3
S3
P5,6
S4
B7
D1
Figure 21 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.
88 Storage overview
B2 B3
B6 B7
D2 D3
D6 D7
B2 B3
B6 B7
B2 P1,2
B4
P3,4
B5 B6
P7,8
B8
D2 D3
15316
B4
B8
D4
D8
B4
B8
15315
Disadvantages
Expensive (half of the drives are used for fault
tolerance).
Only half of total drive capacity usable for data
storage.