  Erasure correcting codes are widely used to ensure data persistence in
distributed storage systems. This paper addresses the simultaneous repair of
multiple failures in such codes. We go beyond existing work (i.e., regenerating
codes by Dimakis et al.) by describing (i) coordinated regenerating codes (also
known as cooperative regenerating codes) which support the simultaneous repair
of multiple devices, and (ii) adaptive regenerating codes which allow adapting
the parameters at each repair. Similarly to regenerating codes by Dimakis et
al., these codes achieve the optimal tradeoff between storage and the repair
bandwidth. Based on these extended regenerating codes, we study the impact of
lazy repairs applied to regenerating codes and conclude that lazy repairs
cannot reduce the costs in term of network bandwidth but allow reducing the
disk-related costs (disk bandwidth and disk I/O).
