Achievable Lower Bound on the Optimal Access Bandwidth of (K+2, K, 2)-MDS Array Code with Degraded Read Friendly

Regenerating codes are designed to reduce the repair bandwidth (access bandwidth) for rebuilding a fail node in an erasure-coded storage system. In practical systems, the fail node is not rebuilt immediately. Before its rebuilding, the data originally stored in the failed node might be accessed by the system. Hence, accessing the data in the failed disk (degraded read) with low latency is crucial for any practical storage system. In this work, to solve this problem, a new class of the regenerating codes based on the maximum distance separable (MDS) array codes is defined, named the MDS array code with the property of degraded read friendly (DRF). For the DRF MDS array codes with 2 redundant nodes and the sub-packetization level of 2, the lower bound of their access bandwidth is derived. A class of the DRF MDS array codes that achieves the derived bound is given to solidify the achievability of the proposed lower bound.