Efficient updates in cross-object erasure-coded storage systems

In the past few years erasure codes have been increasingly embraced by distributed storage systems as an alternative for replication, since they provide high fault-tolerance for low overheads. Erasure codes, however, have few shortcomings that need to be addressed to make them a complete solution for networked storage systems. Lack of support for efficient data repair and data update are the two most notable shortcomings. We recently proposed to use a 2-dimensional product code-Reed-Solomon coding per object and simple XORing across objects- and showed that at a reasonable storage overhead, it can greatly reduce the repair cost. In this paper we propose an efficient approach to handle data updates in cross-object erasure-coded storage systems. Our proposed solution has been implemented and experimentally evaluated. Our results show that compared to the naive approach (re-encoding the data), our proposed scheme can considerably decrease the update cost, especially for when the number of updated blocks is small.