AMCC 9500S User Manual

Understanding RAID Levels and Concepts

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RAID 10 is a combination of striped and mirrored arrays for fault tolerance 
and high performance.

When drives are configured as a striped mirrored array, the disks are 
configured using both RAID 0 and RAID 1 techniques, thus the name RAID 
10 (see Figure ?). A minimum of four drives are required to use this 
technique. The first two drives are mirrored as a fault tolerant array using 
RAID 1. The third and fourth drives are mirrored as a second fault tolerant 
array using RAID 1. The two mirrored arrays are then grouped as a striped 
RAID 0 array using a two tier structure. Higher data transfer rates are 
achieved by leveraging TwinStor and striping the arrays. 

In addition, RAID 10 arrays offer a higher degree of fault tolerance than 
RAID 1 and RAID 5, since the array can sustain multiple drive failures 
without data loss. For example, in a twelve-drive RAID 10 array, up to six 
drives can fail (half of each mirrored pair) and the array will continue to 
function. Please note that if both halves of a mirrored pair in the RAID 10 
array fail, then all of the data will be lost.