Importance

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Abstract

A storage management mechanism maintains parity records on the storage units it services, and includes a status map indicating, for each data block, the location of the corresponding parity block, and the status of the data block. If a single storage unit fails, the mechanism is placed in a failure operating mode while the system continues to operate. While in failure operating mode, storage management verifies status before accessing data on the failed storage unit. If the data has not yet been reconstructed, storage management first reconstructs the data block by successively reading and accumulating an Exclusive-OR of the corresponding blocks on all other storage units in the parity group. The reconstructed data block is then stored in the location of the parity block, and the status map is updated to indicate that the block has been reconstructed. Once the data has been reconstructed, it is only necessary to read from or write to the former parity block directly. Storage management will similarly reconstruct a block of storage on the failed unit before writing to any corresponding block on a non-failed unit, if the block has not yet been reconstructed. In an alternate embodiment, spare areas of storage in the non-failing storage units are allocated to the reconstructed data. The total of these spare areas constitute a virtual spare storage unit. As data is reconstructed, it is placed in the virtual spare unit, and parity is maintained in the normal fashion.

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First Claim