  A new class of exact-repair regenerating codes is constructed by stitching
together shorter erasure correction codes, where the stitching pattern can be
viewed as block designs. The proposed codes have the "help-by-transfer"
property where the helper nodes simply transfer part of the stored data
directly, without performing any computation. This embedded error correction
structure makes the decoding process straightforward, and in some cases the
complexity is very low. We show that this construction is able to achieve
performance better than space-sharing between the minimum storage regenerating
codes and the minimum repair-bandwidth regenerating codes, and it is the first
class of codes to achieve this performance. In fact, it is shown that the
proposed construction can achieve a non-trivial point on the optimal
functional-repair tradeoff, and it is asymptotically optimal at high rate,
i.e., it asymptotically approaches the minimum storage and the minimum
repair-bandwidth simultaneously.
