  In this paper, we study distributed storage problems over unidirectional ring
networks, whose storage nodes form a directed ring and data is transmitted
along the same direction. The original data is distributed to store on these
nodes. Each user can connect one and only one storage node to download the
total data. A lower bound on the reconstructing bandwidth to recover the
original data for each user is proposed, and it is achievable for arbitrary
parameters. If a distributed storage scheme can achieve this lower bound with
equality for every user, we say it an optimal reconstructing distributed
storage scheme (ORDSS). Furthermore, the repair problem for a failed storage
node in ORDSSes is under consideration and a tight lower bound on the repair
bandwidth is obtained. In particular, we indicate the fact that for any ORDSS,
every storage node can be repaired with repair bandwidth achieving the lower
bound with equality. In addition, we present two constructions for ORDSSes of
arbitrary parameters, called MDS construction and ED construction,
respectively. Particularly, ED construction, by using the concept of Euclidean
division, is more efficient by our analysis in detail.
