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Fibre to SAS/SATA II RAID Subsystem
14 User Manual
RAID 6 is similar to RAID 5 in that data protection is achieved by writing parity
information to the physical drives in the array. With RAID 6, however, two sets of parity
data are used. These two sets are different, and each set occupies a capacity equivalent
to that of one of the constituent drives. The main advantage of RAID 6 is High data
availability – any two drives can fail without loss of critical data.
In summary:
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RAID 0 is the fastest and most efficient array type but offers no fault-tolerance. RAID
0 requires a minimum of one drive.
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RAID 1 is the best choice for performance-critical, fault-tolerant environments. RAID
1 is the only choice for fault-tolerance if no more than two drives are used.
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RAID 3 can be used to speed up data transfer and provide fault-tolerance in single-
user environments that access long sequential records. However, RAID 3 does not
allow overlapping of multiple I/O operations and requires synchronized-spindle drives
to avoid performance degradation with short records. RAID 5 with a small stripe size
offers similar performance.
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RAID 5 combines efficient, fault-tolerant data storage with good performance
characteristics. However, write performance and performance during drive failure is
slower than with RAID 1. Rebuild operations also require more time than with RAID 1
because parity information is also reconstructed. At least three drives are required
for RAID 5 arrays.
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RAID 6 is essentially an extension of RAID level 5 which allows for additional fault
tolerance by using a second independent distributed parity scheme (two-dimensional
parity). Data is striped on a block level across a set of drives, just like in RAID 5, and
a second set of parity is calculated and written across all the drives; RAID 6 provides
for an extremely high data fault tolerance and can sustain multiple simultaneous
drive failures. It is a perfect solution for mission critical applications.