In practical large-scale distributed storage systems, node failures are unavoidable. It is therefore desirable to quickly recreate the failed nodes in order to maintain the system integrity. In this letter, we consider a family of erasure codes that provide uncoded repair, where the failed node is regenerated by transfer of data without extra arithmetic operations.

We introduce flexible fractional repetition (FFR) code, of which the coding scheme is a concatenation of an outer MDS code and an inner repetition code. Our proposed codes are applicable to the heterogeneous network environment where node storage capacities and packet repetition degrees vary in a wide range. We present explicit constructions of FFR codes by utilizing combinatorial designs. We further propose a heuristic code construction. Evaluation results show that FFR codes outperform regenerating codes in node repair efficiency.

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