Repairing Erasure Codes

Distributed storage systems introduce redundancy to increase reliability. When erasure coding is used, the exact repair problem arises: if a node storing encoded information fails, in order to maintain the same level of reliability we need to create encoded information at a new node. This amounts to a partial recovery of the code, whereas conventional erasure coding focuses on the complete recovery of the information from a subset of encoded packets. The consideration of the repair network traffic gives rise to new design challenges. Recently, it was established that maintenance bandwidth can be reduced by orders of magnitude compared to standard erasure codes using network coding techniques. We discuss this work in progress and several theoretical and practical challenges on designing erasure codes specifically for storage systems when maintenance communication matters.