NAS System
10
User’s Manual
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 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 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.
1.4 Array Definition
1.4.1 Drive Group
