RAID6 systems instead of storing only one parity and error correction information store two, which are arranged in such a way that even if one of the hard disk drives fails during the data recovery process, the systems continues operational, with no data loss.

On Figure 2 you can see the probability of data loss during a data recovery procedure on RAID0 (in blue), RAID5 (in yellow the probability of hard disk drive failure and in pink the probability of a system failure) and RAID6 (in light blue).

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Figure 2: RAID0, RAID5 and RAID6 comparison.

The “y” axis shows the number of months until a unrecoverable failure while the “x” axis shows the system capacity, in GB.

As you can see on the graph, RAID6 only has the same failure probability of RAID5 on systems starting at 23 TB, below this point RAID6 presents a failure probability far lower than RAID5, being the recommended system for storage systems where reliability is the key word.