Raid 6 (Striping With Dual Distributed Parity); Figure 6. Example Of Raid 5 (Single Virtual Disk With 5 Drives) - Dell POWEREDGE RADI H700 Technical Manual

Dell
Data 1
Parity
Data 5
Generation
Data 9
Data 13
4 parity
Drive 1
Figure 6.
Advantages of RAID 5

Most efficient use of drive capacity of all the redundant RAID configurations

High read transaction rate

Medium-to-high write transaction rate
Disadvantages of RAID 5

Disk failure has a medium impact on throughput

Most complex controller design

Retrieval of parity information after a drive failure takes longer than with mirroring
5.3.4

RAID 6 (Striping With Dual Distributed Parity)

RAID 6 provides data redundancy by using data striping in combination with parity information. See
Figure 7. Similar to RAID 5, the parity is distributed within each stripe. RAID 6, however, uses an
additional physical disk to maintain parity, such that each stripe in the disk group maintains two disk
blocks with parity information. The additional parity provides data protection in the event of two
disk failures.
Figure 7 depicts the RAID 6 data layout. The second set of parity drives are denoted by Q. The P
drives follow the RAID 5 parity scheme. The parity blocks on Q drives are computed using Galois Field
mathematics. There is no performance hit on read operations. However, as a second independent
parity data needs to be generated for each write operation, there is a performance hit during write.
Due to dual data protection, a RAID 6 VD can survive the loss of two drives or the loss of a drive when
one of its drives is being rebuilt.
DELL PERC H700 and H800 Technical Guide
Data 2
Data 6
Data 10
3 parity
Data 17
Drive 2
Example of RAID 5 (Single Virtual Disk with 5 drives)
Data 3 Data 4
1 parity
Data 7
2 parity Data 11
Data 14
Data 15
Data 19
Data 18
Drive 3 Drive 4
0 parity
Data 8
Data 12
Data 16
Data 20
Drive 5
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