Learn in the textbookSystem Configurations for Availability and Reliability
DefinitionRAID combines several disks so they can be handled as one, and uses the way data is placed across them to gain speed or fault tolerance.
ExplanationThe ways of placing data are identified by numbers called RAID levels (RAID レベル), and each level strikes a different balance between speed, resistance to failure and usable capacity. The parity (パリティ) in RAID5 is recovery information calculated from the data, so if one disk's worth is lost, the original contents can be recalculated from it and the remaining data.
AnalogyIf you keep a separate slip with just the total of three people's scores, losing one person's slip is no problem: subtract the other two scores from the total to get it back.
Memory hookThe R in RAID stands for Redundant. Only level 0 has zero redundancy, which matches its number.