  We introduce a new class of exact Minimum-Bandwidth Regenerating (MBR) codes
for distributed storage systems, characterized by a low-complexity uncoded
repair process that can tolerate multiple node failures. These codes consist of
the concatenation of two components: an outer MDS code followed by an inner
repetition code. We refer to the inner code as a Fractional Repetition code
since it consists of splitting the data of each node into several packets and
storing multiple replicas of each on different nodes in the system.
  Our model for repair is table-based, and thus, differs from the random access
model adopted in the literature. We present constructions of Fractional
Repetition codes based on regular graphs and Steiner systems for a large set of
system parameters. The resulting codes are guaranteed to achieve the storage
capacity for random access repair. The considered model motivates a new
definition of capacity for distributed storage systems, that we call Fractional
Repetition capacity. We provide upper bounds on this capacity while a precise
expression remains an open problem.
