Accusys ExaRAID GUI - Manual (Page 257)

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.