NAND Flash Memory/ReRAM Hybrid Unified Solid-State-Storage Architecture

The proposed unified solid-state storage (USSS) with hybrid NAND flash memory/ReRAM provides high system-level data protection. In the conventional storage system, the hierarchical storage architecture (Server/Disk array/SSD/NAND flash memory) has duplicated functions. USSS solves this structural problem of the conventional enterprise-storage systems. The proposed unified storage controller integrates the duplicated functions (error corrections and redundancies). Five highly reliable techniques are presented; reverse-mirroring (RM), shift-mirroring (SM), error-reduction synthesis (ERS), page-RAID, and error-masking (EM). SM is a modified technique from RM with no ReRAM buffer. These technologies utilize error-patterns asymmetries of the NAND flash memory and fast, page-rewritable and high endurance ReRAM. RM, SM and EM are the mirroring techniques to reduce bit-errors of the NAND flash memory by intelligently allocating the write address and comparing the data in the primary/mirrored NAND flash memories, respectively. The page-RAID generates the block-parity in each block and EM records the error-location during read. Without mirroring, the acceptable raw BER of the NAND flash memory (ABER) increases by 4.4×. Moreover, when RM, ERS, page-RAID, and EM are applied, the ABER increases by 32×. This corresponds to an increase of the endurance or the data-retention time of the NAND flash memory by 4.2 or 34×.