Users Guide

Spanned RAID levels
Spanning is a term used to describe the way in which RAID levels 10, 50, and 60 are constructed from multiple sets of basic, or simple RAID
levels. For example, a RAID 10 has multiple sets of RAID 1 arrays where each RAID 1 set is considered a span. Data is then striped (RAID 0)
across the RAID 1 spans to create a RAID 10 virtual disk. Similarly, RAID 50 and RAID 60 combine multiple sets of RAID 5 or RAID 6
respectively with striping.
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 26. Example of Distributed Parity (RAID 5)
NOTE
: Parity is distributed across multiple physical disks in the disk group.
Figure 27. Example of Dual Distributed Parity (RAID 6)
NOTE
: Parity is distributed across all disks in the array.
114 Appendix RAID description