RAID

RAID 6: Independent Data Disks with Double Parity
Based on RAID 5 this variant is designed solely to improve data redundancy with parity data written to two separate disks. Where most RAID types can tolerate the loss of a single drive from the array, RAID 6 is able to recover from the loss of two drives failing. Some performance is lost over RAID 5 due to the additional calculations although random read times may be slightly improved as data is spread over an additional disk.

A minimum of 4 drives are required for this type of array as is a specialized (read expensive) dedicated controller card. For this reason RAID 6 is infrequently used, the chances of 2 disks failing simultaneously being so slim except in situations where the entire array fails in which case no amount of error correction will help.

RAID 7: Asynchronous, cached striping with dedicated parity
Unlike the variants listed above RAID 7 is not an industry standard, instead it is the trademarked solution of a single company, Storage Computer Corporation, who use it to describe their proprietary RAID design.

RAID 7 is based on RAID 3 and 4 but with enhancements to solve some of the issues surrounding their performance, the largest enhancement is the inclusion of a large amount of cache arranged on multiple levels and a special dedicated processor to manage the array asynchronously in real time. The additional hardware support allows the array to support many simultaneous processes in turn boosting both read and write performance whilst maintaining the integrity of the data and fault tolerance. Simply put, the additional hardware removes much of the burden placed onto the array by the parity calculations and parity drive.

However, despite the increase in performance RAID 7 remains a very expensive solution, produced by only one company and is vulnerable to power cuts which erase cached information.