Three-dimensional RAID Arrays with Fast Repairs

Large data storage systems often use Reed-Solomon erasure codes to protect their static data against triple or even quadruple device failures. A main drawback of this approach is the high cost of recovering the contents of failed devices, as it requires accessing the contents of a large number of surviving devices. We present a three-dimensional RAID organization that adds vertical parity devices to a stack of identical two-dimensional RAID arrays. These new vertical parity devices will let the organization recover faster from all single device failures while greatly reducing the risk of data loss. Depending on the way the vertical parities are defined, the new arrays will either toler-ate all triple failures and more than 99.9 percent of all quadruple failures, or all quintuple failures and more than 99.995 percent of all sextuple failures.