Reliability-availability-serviceability characteristics of a compressed-memory system

New compression innovations and high-density silicon technology enable us to introduce main-memory compression. This technology is able to achieve, in most cases, 2:1 or better compression without impacting performance. It provides an enormous cost/performance advantage, given the cost content of memory in modern enterprise servers. The complex and highly parallel data manipulations central to this compression implementation would, if unprotected by extensive error detection and error correction techniques, offer several potential data integrity exposures. This paper describes the memory subsystem of an enterprise class server with a compressed mainstore and the methods which have been employed to guarantee the integrity of the compressed data. These methods consist of a novel ECC algorithm which includes address information in the code words, the use of CRC codes for compressed data blocks, and various consistency checks on the memory management structures used in the management of a compressed mainstore.