Intel AFCSASRISER User Guide - Page 25

RAID IME, Example of Distributed Parity across Two Blocks in a Stripe RAID 6

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Strong Points Weak Points Drives Provides data redundancy, high read rates, and 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. 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. 3 to 32 The following figure shows a RAID 6 data layout. The second set of parity drives are denoted by Q. The P drives follow the RAID 5 parity scheme. RAID IME Segment 1 Segment 6 Segment 11 Segment 16 Parity (P17-P20) Segment 2 Segment 3 Segment 4 Segment 7 Segment 8 Parity (P5-P8) Segment 12 Parity (P9-P12) Parity (Q9,ÄìQ1 Parity (P13-P16) Parity (Q13-Q16) Segment 13 Parity (Q17-Q20) Segment 17 Segment 18 Parity (P1-P4) Parity (Q5-Q8) Segment 9 Segment 14 Segment 19 Parity (Q1-Q4) Segment 5 Segment 10 Segment 15 Segment 20 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. Figure 4. Example of Distributed Parity across Two Blocks in a Stripe (RAID 6) An IME volume can be configured with up to ten mirrored disks (one or two global hot spares can also be added). Figure 5 shows the logical view and physical view of an Integrated Mirroring Enhanced (IME) volume with three mirrored disks. Each mirrored stripe is written to a disk and mirrored to an adjacent disk. This type of configuration is also called RAID 1E. Intel® RAID Software User's Guide 13

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Intel
®
RAID Software User’s Guide
13
The following figure shows a RAID 6 data layout. 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)
RAID IME
An IME volume can be configured with up to ten mirrored disks (one or two global hot spares
can also be added).
Figure 5
shows the logical view and physical view of an Integrated
Mirroring Enhanced (IME) volume with three mirrored disks. Each mirrored stripe is written
to a disk and mirrored to an adjacent disk. This type of configuration is also called RAID 1E.
Strong Points
Provides data redundancy, high read rates, and 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