System information

A-1
Appendix A: Understanding RAID
A.1 RAID Overview
The controller supports eleven types of RAID: RAID 0, 1, 3, 5, 6, 10, 30, 50, 60, JBOD and NRAID. The application(s) you
are using will determine which RAID setup is best for you.
• RAID Level 0
This level offers high transfer rates and is ideal for large blocks of data where speed is of the essence. Computer Aided
Design, graphics, scientific computing, image, and multimedia applications are all good examples. If one drive in a RAID
0 array fails, the entire data array is lost.
• RAID Level 1
This level may be an appropriate choice if cost and performance are of significantly less importance than fault tolerance
and reliability.
• RAID Level 3
This level is similar to the more commonly used level 5. Both offer a good level of fault tolerance and overall system
reliability at a reasonable cost for redundancy overhead. RAID 3 is useful for large file sequential writes such as video
applications.
• RAID Level 5
This level offers high I/O transaction rates and is the ideal choice when used with on-line transaction processing
applications, such as those used in banks, insurance companies, hospitals, and all manner of office environments. These
applications typically perform large numbers of concurrent requests, each of which makes a small number of disk
accesses. If one drive in a RAID level 5 array fails, the lost data can be rebuilt from data on the functioning disks.
• RAID Level 6
This level is similar to level 5. Data is striped across all member disks and parity is striped across all member disks, but
RAID 6 has two-dimensional parities, so it can tolerate double-disk failure.
• JBOD ("Just a Bunch of Disks")
This is a method of arranging multiple disks and, technically, is not RAID. Under JBOD, all disks are treated as a single
volume and data is “spanned” across them. JBOD provides no fault tolerance or performance improvements over the
independent use of its constituent drives.
• NRAID ("None RAID")
This level allows you to combine the capacity of all drives and does not suffer from data redundancy.
• RAID Level 10
This level offers a compromise between the reliability and tolerance of level 1 and the high transfer rates provided by
level 0.
• RAID Level 30/50/60
RAID 30/50/60 performs striping over RAID 3/5/6 groups. With multiple independent RAID groups, performance and
reliability can be improved. These RAID levels are supported by data striping volumes over logical disks.