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For example, if three drives are arranged in RAID 3, this gives an array space efficiency of 1 − 1/n = 1 − 1/3 = 2/3 ≈ 67%; thus, if each drive in this example has a capacity of 250 GB, then the array has a total capacity of 750 GB but the capacity that is usable for data storage is only 500 GB.
A RAID 0 setup can be created with disks of differing sizes, but the storage space added to the array by each disk is limited to the size of the smallest disk. For example, if a 120 GB disk is striped together with a 320 GB disk, the size of the array will be 120 GB × 2 = 240 GB.
CLARiiON was an early commercial example of a RAID product and initially sold exclusively as an array with the company's Aviion line of computer systems as the HADA (High Availability Disk Array) and later the HADA II [6] before being made available for broader open systems attachment and renamed CLARiiON in 1994. [7]
The four-drive example is identical to a standard RAID 1+0 array, while the three-drive example is a software implementation of RAID 1E. The two-drive example is equivalent to RAID 1. [13] The driver also supports a "far" layout, in which all the drives are divided into f sections. All the chunks are repeated in each section but are switched in ...
RAID 6 requires a minimum of four disks. As with RAID 5, a single drive failure results in reduced performance of the entire array until the failed drive has been replaced. [11] With a RAID 6 array, using drives from multiple sources and manufacturers, it is possible to mitigate most of the problems associated with RAID 5.
Those RAID systems made their way to the consumer market, for users wanting the fault-tolerance of RAID without investing in expensive SCSI drives. Fast consumer drives make it possible to build RAID systems at lower cost than with SCSI, but most ATA RAID controllers lack a dedicated buffer or high-performance XOR hardware for parity calculation.
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In some RAID configurations, such as RAID 0, failure of a single member drive of the RAID array causes all stored data to be lost. In other RAID configurations, such as a RAID 5 that contains distributed parity and provides redundancy , if one member drive fails the data can be restored using the other drives in the array.