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Dell PowerEdge RAID Controller 11 User’s Guide PERC H755, H750, H355, and H350 Controller Series

Parity data

Parity data is redundant data that is generated to provide fault tolerance within certain RAID levels. In the event of a disk failure, the parity data can be used by the controller to regenerate user data. Parity data is present for RAID 5, 6, 50, and 60.

The parity data is distributed across all the physical disks in the system. If a single physical disk fails, it can be rebuilt from the parity and the data on the remaining physical disks. RAID level 5 combines distributed parity with disk striping. Parity provides redundancy for one physical disk failure without duplicating the contents of the entire physical disks.

RAID 6 combines dual distributed parity with disk striping. This level of parity allows for two disk failures without duplicating the contents of entire physical disks.

Figure 1. Example of Distributed Parity (RAID 5)
The figure shows an example of distributed parity.
NOTE:Parity is distributed across multiple physical disks in the disk group.
Figure 2. Example of Dual Distributed Parity (RAID 6)
The figure shows an example of dual distributed parity.
NOTE:Parity is distributed across all disks in the array.

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