Using device diversity to protect data against batch-correlated disk failures

Batch-correlated failures result from the manifestation of a common defect in most, if not all, disk drives belonging to the same production batch. They are much less frequent than random disk failures but can cause catastrophic data losses even in systems that rely on mirroring or erasure codes to protect their data. We propose to reduce impact of batch-correlated failures on disk arrays by storing redundant copies of the same data on disks from different batches and, possibly, different manufacturers. The technique is especially attractive for mirrored organizations as it only requires that the two disks that hold copies of the same data never belong to the same production batch. We also show that even partial diversity can greatly increase the probability that the data stored in a RAID array will survive batch-correlated failures.