Users guide

13 Intel® RAID Software User Guide
Table 4. RAID 6 Overview
The following figure shows a RAID 6 data layo
ut. The second set of parity drives are
denoted by Q. The P drives follow the RAID 5 parity scheme.
Figure 4. Example of Distributed Parity across Two Blocks in a Stripe (RAID
6)
Uses
Provides a high level of data protection through the use of a second parity
block in each stripe. Use RAID 6 for data that requires a high level of
protection from loss.
In the case of a failure of one drive or two drives in a virtual disk, the RAID
controller uses the parity blocks to recreate the missing information. If two
drives in a RAID 6 virtual disk fail, two drive rebuilds are required, one for
each drive. These rebuilds do not occur at the same time. The controller
rebuilds one failed drive at a time.
Use for office automation and online customer service that requires fault
tole
rance. Use for any application that has high read request rates but low
write request rates.
Strong Points
Provides data redundancy, high read rates, an
d good performance in most
environments. Can survive the loss of two drives or the loss of a drive while
another drive is being rebuilt. Provides the highest level of protection against
drive failures of all of the RAID levels. Read performance is similar to that of
RAID 5.
Weak Points
Not well suited to tasks requiring lot of writes. A RAID 6 virtual disk has to
generate two sets of parity data for each write operation, which results in a
significant decrease in performance during writes. Disk drive performance is
reduced during a drive rebuild. Environments with few processes do not
perform as well because the RAID overhead is not offset by the performance
gains in handling simultaneous processes. RAID 6 costs more because of
the extra capacity required by using two parity blocks per stripe.
Drives
3 to 32
Segment 1
Segment 6
Segment 2
Segment 7
Segment 3
Segment 8
Segment 4
Parity (P5-P8)
Parity (P1-P4)
Parity (Q5-Q8)
Parity (Q9–Q1
Parity (Q1-Q4)
Segment 5
Parity is distributed across all drives in the array. When only three hard drives are available for
RAID 6, the situation has to be that P equals Q equals original data, which means that the original
data has three copies across the three hard drives.
Segment 10
Parity (P9-P12)
Segment 9
Segment 12
Segment 11
Segment 16
Parity (P17-P20)
Parity (P13-P16)
Segment 19
Segment 15
Segment 17
Segment 13
Segment 18
Segment 14
Parity (Q17-Q20)
Parity (Q13-Q16)
Segment 20