Sans Digital Mobileraid MR8X, Detailed User'S Manual

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SAS-to-SATA II RAID Subsystem
Installation and Configuration Manual
18
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.
Š
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.
Š
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.
Š
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.
Š
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.
RAID Management
The subsystem can implement several different levels of RAID technology. RAID levels
supported by the subsystem are shown below.
RAID Level Description Min. Drives
0
Block striping is provide, which yields higher
performance than with individual drives. There
is no redundancy.
1
1
Drives are paired and mirrored. All data is 100%
duplicated on an equivalent drive. Fully
redundant.
2
3
Data is striped across several physical drives.
Parity protection is used for data redundancy.
3
5
Data is striped across several physical drives.
Parity protection is used for data redundancy. 3
6
Data is striped across several physical drives.
Parity protection is used for data redundancy.
Requires N+2 drives to implement because of
two-dimensional parity scheme
4
0 + 1
Combination of RAID levels 0 and 1. This level
provides striping and redundancy through
mirroring.
4