OpenEye G4 GraniteRack, Руководство по оборудованию, Страница: 27 / 30

31822AE 27
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.
Dual-level RAID achieves a balance between the increased data availability inherent in RAID 1 and
RAID 5 and the increased read performance inherent in disk striping (RAID 0). These arrays are
sometimes referred to as RAID 0+1 (or RAID 10), and RAID 0+5 (or RAID 50).
In summary:
•
RAID 0 is the fastest and most efficient array type, but offers no fault tolerance. RAID 0
requires a minimum of two drives.
•
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.
•
RAID 3 can be sued 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.
•
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.
•
RAID 6 is essentially an extension of RAID 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.