SSCMSD - Single-Symbol Correction Multi-symbol Detection for DRAM Subsystem

Abstract

As DRAM technology continues to evolve towards smaller feature sizes and increased densities, faults in DRAM subsystem are becoming more severe. Current servers mostly use CHIPKILL based schemes to tolerate up-to one/two symbol errors per DRAM beat. Multi-symbol errors arising due to faults in multiple data buses and chips may not be detected by these schemes. In this paper, we introduce Single Symbol Correction Multiple Symbol Detection (SSCMSD) - a novel error handling scheme to correct single-symbol errors and detect multi-symbol ones. Here, we use a hash in combination with ECC to avoid silent data corruptions (SDCs). We employ 32-bit Spookyhash along with Reed-Solomon code to implement SSCMSD for a x4 based DDRx system. Our simulations show that the proposed scheme effectively prevents SDCs in the presence of multiple symbol errors. For this design, we need 19 chips per rank (storage overhead of 18.75 percent), 76 data bus-lines and additional hash-logic at the memory controller.