Redundancy is additional information stored along with the data that allows the controller to reconstruct lost data.
RAID 1 uses mirroring for redundancy. RAID 3 and RAID 5 use redundancy information, sometimes called parity, that is constructed from the data bytes and striped along with the data on each disk.
A redundancy check, performed using the Array >> Check Redundancy option:
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For more information, see Checking Data Redundancy on an Array on the How To tab.