Abstract

A data storage system including k data drives and n-k redundant drives performs a write operation to a designated sector on a data drive by (i) retrieving from each of the other data drives the data stored in a corresponding sector, (ii) encoding the symbols stored in corresponding storage locations using an (n,k) distance D Reed-Solomon code to generate, for each set of k symbols, n-k redundancy symbols, and (iii) recording the generated symbols in the corresponding storage locations on each of the redundant drives. When the system next performs a write operation directed to the designated sector or one of the corresponding sectors on the other data drives, the system records the data on the appropriate sector and simultaneously records the same data in a corresponding sector on one of the redundant drives. The system continues writing to these sectors and associated redundant drives without performing retrieval and encoding operations, until the corresponding sectors on [(n-k)/2]-1 different data drives have been involved in write operations. When the system next performs a write operation directed to a corresponding sector on another data drive, the system retrieves the corresponding data from all k data drives, encodes the symbols in corresponding storage locations to generate redundancy symbols and stores the redundancy symbols in the corresponding storage locations on the redundant drives.