Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 21)

Understanding RAID Levels and Concepts
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RAID 6
RAID 6 provides greater redundancy and fault tolerance than RAID 5. It is
similar to RAID 5 but, instead of a single block, RAID 6 has two blocks of
parity information (P+Q) distributed across all the drives of a unit (see
Figure 4).
Due to the two parities, a RAID 6 unit can tolerate two hard drives failing
simultaneously. This also means that a RAID 6 unit can be in two different
states at the same time. For example, one subunit can be degraded while
another is rebuilding, or one subunit can be initializing while another is
verifying.
The 3ware implementation of RAID 6 requires a minimum of five drives.
Performance and storage efficiency also increase as the number of drives
increase.
Figure 4. RAID 6 Configuration Example
RAID 10
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 (see Figure 5). 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
(600 GB - 240 GB for 2 parity drives)