Parity checking enables Tape RAID Level 5 backup to recreate lost data if one of the drives fail. With parity checking, when data is written to an array of drives, an extra data element, called parity, is added to the stored data. The parity check uses Boolean logic to recreate lost data. For example, if you are using a RAID consisting of three drives. When you perform a backup, for every two elements of ordinary data, the third element (parity) is added. If the drive containing the second data element is damaged, data from the lost drive can be recreated using the parity data element and the data elements from the remaining two drives by applying Boolean logic.
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