2.4.11 Parity; Example Of Distributed Parity (Raid 5); Types Of Parity - Lenovo ThinkServer RD240 Software User's Manual

2.4.11 Parity

Segment 1 Segment 2
Segment 7 Segment 8
Segment 13 Segment 14
Segment 19 Segment 20
Segment 25
Parity (21-25)
Parity (26–30) Segment 26
Note: Parity is distributed across all drives in the drive group.
Parity generates a set of redundancy data from two or more parent data
sets. The redundancy data can be used to reconstruct one of the parent
data sets in the event of a drive failure. Parity data does not fully
duplicate the parent data sets, but parity generation can slow the write
process. In RAID, this method is applied to entire drives or stripes across
all of the drives in a drive group. The types of parity are described in
Table 2.1.
Table 2.1

Types of Parity

Parity Type Description
Dedicated The parity data on two or more drives is stored on an
additional disk.
Distributed The parity data is distributed across more than one drive in
the system.
RAID 5 combines distributed parity with disk striping. If a single drive
fails, it can be rebuilt from the parity and the data on the remaining
drives. An example of a RAID 5 drive group is shown in
5 uses parity to provide redundancy for one drive failure without
duplicating the contents of entire drives. RAID 6 uses distributed parity
and disk striping, also, but adds a second set of parity data so that it can
survive up to two drive failures.
Figure 2.3

Example of Distributed Parity (RAID 5)

Segment 3
Segment 9
Segment 15
Parity (16-20)
Segment 21
Segment 27
Components and Features
Segment 4 Segment 5
Segment 10 Parity (6-10)
Segment 11
Parity (11–15)
Segment 16 Segment 17
Segment 22 Segment 23
Segment 28 Segment 29
Figure 2.3. RAID
Parity (1-5)
Segment 6
Segment 12
Segment 18
Segment 24
Segment 30
2-9