Graftage Coding for Distributed Storage Systems

To achieve various tradeoffs between storage and repair bandwidth, this article proposes to construct exact repair codes by grafting two codes C1 and C2. By replacing certain nonzero entries in the generator matrix of C1 by zero, the repair bandwidth of the resulting grafting part decreases. However, it may no longer keep the maximum-distance-separable (MDS) property. As a result, the grafted code C2 takes these nonzero entries into account such that the entire graftage code can keep the MDS property. The relationship between the bandwidth reduction of C1 and the file size of C2 is derived to optimize graftage codes. Our analysis indicates that these graftage codes may provide better tradeoffs than space-sharing.