describes a storage solution in which part of the storage capacity stores redundant information about user data stored on the remainder of the storage capacity. The redundant information enables regeneration of user data if one of the in the fails.
RAID relies on a series of configurations, called levels, to determine how user data and data are written to and retrieved from the disk drives. RAID Level 1, RAID Level 3, RAID Level 5, and RAID Level 6 write redundancy data to the disk drive media for fault tolerance. The redundancy data might be a copy of the data (mirrored) or an error correcting code derived from the data. If a disk drive fails, you can use the redundancy data to quickly reconstruct information on a replacement disk drive.
RAID Level | Data Protection Available |
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RAID Level 5 or RAID Level 6 |
or are best for multiuser environments, such as database or file system storage, where typical I/O size is small, and a high proportion of read activity exists. RAID Level 5 and RAID Level 6 are the most cost-effective RAID levels that provide redundancy protection. If a single disk drive fails in a RAID Level 5 or RAID Level 6 array, all of the associated logical drives become degraded, but the redundant information enables the data to be accessed. If two or more disk drives fail in a RAID Level 5 array, all of the associated logical drives fail, and all data is lost. If three or more disk drives fail in a RAID Level 6 array, all of the associated logical drives fail, and all data is lost. |
RAID Level 3 |
is best for large data transfers in software applications, such as multimedia or medical imaging, that write and read large sequential chunks of data. RAID Level 3 offers redundancy protection, but any two disk drive failures in the same array result in data loss. If a single disk drive fails in a RAID Level 3 array, all of the associated logical drives become degraded, but the redundant information enables the data to be accessed. If two or more disk drives fail in a RAID Level 3 array, all of the associated logical drives fail, and all data is lost. |
RAID Level 1 |
offers high performance and maintains identical copies of data on disk drive pairs, also known as mirrored pairs. Half of the disk drives are available for storing user data. Disk drive pair failure causes data loss. The strength of RAID Level 1 is high safety and data availability. Loss of a mirrored pair of disk drives results in data loss. If a single disk drive fails in a RAID Level 1 array, all of the associated logical drives become degraded, but the mirror disk drive allows the data to be accessed. RAID Level 1 can survive multiple disk drive failures as long as no more than one failure exists per mirrored pair. If a disk drive pair fails in a RAID Level 1 array, all of the associated logical drives fail, and all data is lost. |
RAID Level 0 |
offers high performance, but it does not provide any data redundancy. If a single disk drive fails in a RAID Level 0 array, all of the associated logical drives fail, and all data is lost. |