A Comprehensive Study on RAID-6 Codes: Horizontal vs. Vertical

The RAID-6 architecture is playing an increasingly important role in modern storage systems. There are generally two kinds of RAID-6 codes, horizontal codes and vertical codes. Horizontal codes have been extensively studied and widely implemented, while vertical codes have not gained the equal attention. In this paper, we investigate the state-of-the-art horizontal and vertical RAID-6 codes and select two representative ones, RDP for horizontal codes and P-Code for vertical codes, to compare their performance. Since the code lengths of vertical codes are usually restricted, we first provide two efficient code shortening algorithms for vertical codes, by which the length of a vertical code can be extended to an arbitrary given one. In the context of our code shortening algorithms for vertical codes, we compare the theoretical performance of RDP and P-Code at consecutive lengths, and examine their practical behaviors in the real environment. Theoretical analysis and experimental evaluation results have demonstrated that vertical codes can provide comparable, and sometimes even better, performance than horizontal codes.