Rethinking WOM Codes to Enhance the Lifetime in New SSD Generations.

New generations of Solid State Drives (SSDs) offer increased storage density with higher bits per cell, but an order of magnitude lower Program and Erase (P/E) cycles. This decreases the number of times one can rewrite on the SSD, and hence, the overall lifetime of the drive. One way of improving drive lifetime is by applying Write-Once Memory (WOM) codes which can rewrite on top of pre-existing data without erasing previous data. This increases the total logical data that can be written on the physical medium before an erase operation is required. Traditional WOM codes are not scalable and only offer up to 50% increase in total writable logical data between any two erase operations. In this paper we present a novel, simple and highly efficient family of WOM codes. Although our design is generic and could be applied to any N-Level cell drive, we focus on QLC drives to demonstrate and evaluate the proposed scheme and show that it can increase the total logical writable data before an erase in a range of 50-375% the physical medium capacity with varying storage overheads. Next, we argue that it is possible to further increase the total logical writable data between two erase operations by up to 500% with the help of a carefully chosen internal error-correcting code (ECC) already present in SSDs.