Lenovo ThinkServer RD330 MegaRAID SAS Software User Guide - Page 26
Example of Disk Mirroring RAID 1, Example of Distributed Parity RAID 5, Table 2
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Chapter 2: Introduction to RAID | Components and Features MegaRAID SAS Software User Guide Disk mirroring provides 100 percent redundancy, but is expensive because each drive in the system must be duplicated. Figure 4 shows an example of disk mirroring. 2.4.10 Parity Figure 4: Segment 1 Segment 2 Segment 3 Segment 4 Segment 1 Duplicated Segment 2 Duplicated Segment 3 Duplicated Segment 4 Duplicated Example of Disk Mirroring (RAID 1) 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. Table 2: Types of Parity Parity Type Dedicated Distributed Description The parity data on two or more drives is stored on an additional disk. 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 Figure 5. RAID 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. Segment 1 Segment 7 Segment 13 Segment 19 Segment 25 Parity (26-30) Segment 2 Segment 8 Segment 14 Segment 20 Parity (21-25) Segment 26 Segment 3 Segment 9 Segment 15 Parity (16-20) Segment 21 Segment 27 Segment 4 Segment 10 Parity (11-15) Segment 16 Segment 22 Segment 28 Note: Parity is distributed across all drives in the drive group. Figure 5: Example of Distributed Parity (RAID 5) Segment 5 Parity (6-10) Segment 11 Segment 17 Segment 23 Segment 29 Parity (1-5) Segment 6 Segment 12 Segment 18 Segment 24 Segment 30 Page 26