RAID 5, also known as "parity," is an error-detection method used to detect and correct errors in data transmissions by performing specific checks of the data blocks within a stripe. In the event of a single drive failure, the information for the missing drive or media can be recreated by examining the remaining data and the parity information. This information enables the system to regenerate the missing data bits.
RAID 5 incorporates data striping. With a RAID 5 array using three or more drives, data and parity are striped across all the drives. Data is processed on two drives while the third drive holds the parity information. If one of the data drives is lost, the parity information ensures that the missing data can be recreated.
RAID 5 combines good performance, fault tolerance, high capacity, and storage efficiency. Because of the need for the system to calculate parity information during write activity, RAID 5 is best suited to situations where read activity is much higher than write activity. (For situations where write activity is high, RAID 1 is probably a better choice).
RAID 5 increases the virtual capacity of your media since three drives appear as one virtual drive. For example, if your media’s capacity were two GB, normally you would need two spanning tapes to back up four GB. However, with RAID 5, you can store the same four GB on one virtual media without spanning. If you are using three drives with RAID 5, your storage capacity doubles. If you are using five drives with RAID 5, your perceived storage capacity quadruples.
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