Dual Region Write Buffering: Making Large-Scale Nonvolatile Buffer using Small Capacitor in SSD

Abstract

Write buffering not only enables Solid State Drive (SSD) to immediately respond to the write request but also increases the lifespan of the SSD by reducing the amount of data written to the flash memory. However, since the DRAM which is used as a write buffer is volatile, it has a few critical problems such as buffered data loss upon sudden power-off and limited write reduction effect due to the flush commands and synchronous writes from the file system. These problems can be addressed when non-volatile memory (NVRAM)is used, instead of DRAM, as a write buffer. In this paper, we propose a novel Dual-Region Write Buffering (DRWB) scheme that implements logically non-volatile write buffer using large sized DRAM and small capacity capacitor. The DRWB exploits the differential write scheme, which has been developed originally for the write reduction in SSD, to protect data in the write buffer. Experimental results show that the proposed scheme enables us to achieve the same effect with the NVRAM write buffer, in terms of the data reliability, without noticeable performance degradation.