The paper introduces a new metric called "skip cost" to quantify the number of contiguous sections accessed on a disk during the repair process in distributed storage systems. It then presents three constructions of array codes that achieve zero skip cost:
Construction A: An (M × N, k)-MDS array code with M = 2m packets and N = 2(m + 1) nodes, where k = m + 1. The repair scheme has zero skip cost and optimal rebuilding ratio of 1/2.
Construction B: An (M × N, k)-MDS array code with M = 2m packets and N = k + k/2 + 1 nodes. The code rate is approximately 2/3 for large values of k, and the repair scheme has zero skip cost and optimal rebuilding ratio of 1/2.
Construction C: A generalization of Construction B, where the number of information nodes k does not depend on the sub-packetization level M. This construction achieves zero skip cost and optimal rebuilding ratio for any choice of k and M.
The paper also discusses fractional repetition codes, where the order of points in each node can impact the skip cost. It is shown that at least two-thirds of Steiner quadruple systems (SQS) have locality two and skip cost zero.
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