Parity-Stream Separation and SLC/MLC Convertible Programming for Life Span and Performance Improvement of SSD RAIDs

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Presented at HotStorage 2017 by

Yoohyuk Lim

Jaemin Lee

Cassiano Campes

Euiseong Seo

To reduce the performance and lifespan loss caused by the partial-stripe writes in SSD RAIDs, we propose two schemes: parity-stream separation and SLC/MLC convertible programming. Parity-stream separation splits the parity block stream from the data block stream to decrease valid page copy during garbage collection. In the convertible programming scheme, the flash memory blocks that are allocated for parity data are programmed in SLC mode to reduce the wear caused by programming stress, while the other flash memory blocks are written in MLC mode as usual. Evaluation shows that our scheme decreased garbage collection overhead by up to 58% and improved lifespan by up to 54%, assuming that the MLC write stress was 3.5 times that of the SLC.