Reliability of scrubbing recovery-techniques for memory systems

The authors analyze the problem of transient-error recovery in fault-tolerant memory systems, using a scrubbing technique. This technique is based on single-error-correction and double-error-detection (SEC-DED) codes. When a single error is detected in a memory word, the error is corrected and the word is rewritten in its original location. Two models are discussed: (1) exponentially distributed scrubbing, where a memory word is assumed to be checked in an exponentially distributed time period, and (2) deterministic scrubbing, where a memory word is checked periodically. Reliability and mean-time-to-failure (MTTF) equations are derived and estimated. The results of the scrubbing techniques are compared with those of memory systems without redundancies and with only SEC-DED codes. A major contribution of the analysis is easy-to-use expressions for MTTF of memories. The authors derive reliability functions and mean time to failure of four different memory systems subject to transient errors at exponentially distributed arrival times