  In order to provide high data reliability, distributed storage systems
disperse data with redundancy to multiple storage nodes. Regenerating codes is
a new class of erasure codes to introduce redundancy for the purpose of
improving the data repair performance in distributed storage. Most of the
studies on regenerating codes focus on the single-failure recovery, but it is
not uncommon to see two or more node failures at the same time in large storage
networks. To exploit the opportunity of repairing multiple failed nodes
simultaneously, a cooperative repair mechanism, in the sense that the nodes to
be repaired can exchange data among themselves, is investigated. A lower bound
on the repair-bandwidth for cooperative repair is derived and a construction of
a family of exact cooperative regenerating codes matching this lower bound is
presented.
