Know How: RAID Levels And Glossary
The level of a RAID system (Redundant Array of Inexpensive Disks) relates to its operating mode and how the hard disks are combined to form a single logical drive.
RAID- 0
RAID-0 is not really a RAID level as such, because there is no redundant drive. The data is distributed across the available disks using a process called striping (also called "stripeset"). This technique is used to build a common data area and to achieve higher speeds. The controller merges several hard disks into one large, logical drive. As the data is written and read in a quasi-parallel fashion, overall performance is boosted compared with just a single drive. This is of particular benefit for video editing and image editing programs. However, if one drive fails, you lose the data on all drives.
RAID-1
RAID-1 (mirroring) involves mirroring the complete contents of one hard disk onto another. From the security standpoint, this is ideal (although not cheap), as the redundancy uses 50 percent of your hard disk capacity. There is a marginal increase in performance. Write access is slightly slower, but the controller uses the fastest available disk for reading data.
RAID-3
RAID-3 requires at least three hard disks, one of which is used to store error-correction data. Should a disk fail, the missing data can be restored from the parity and error-detection information on the redundant disk using an allocation algorithm. As RAID-3 interleaves the data across the drives, read speed is good, but writing is slower.
RAID-5
RAID-5 writes the original data and the error-correction information across all available drives (at least three). Writing is thus spread across all the drives in a RAID-5 system, which means that both reading and writing operations may overlap. RAID-5 offers good price/ performance, as only the space equivalent to one disk is allocated to the redundant data.
RAID 0+1
RAID 0+1 is a combination of RAID level 0 and level 1. The disks are combined using the striping technique, and then mirrored. This only makes sense if speed is a priority, since two mirrored drives represent an expensive form of insurance.
