Jesper Berg We are quite used to the fact that technology improves over time, but as many have noted this isn’t always the case with SSDs. In this part of the tech industry, shrinking transistors and higher densities translate to lower costs but also less reliability and in the end, performance. Three researchers from the Department of Computer Science and Engineering at the University of California, San Diego have taken on the unappreciative task of putting this fact on paper. It is called “The Bleak Future of NAND Flash Memory” and is available here. The authors, Laura M. Grupp, John D. Davis, and Steven Swanson, point out that if the current downward trend in flash density continues, all of the advantages of the storage medium will similarly deteriorate.
SSDs will continue to improve by some metrics (notably density and cost per bit), but everything else about them is poised to get worse.
Not surprisingly, this is particularly true for multi-level cell NAND and the even less inspiring triple-level cell NAND.
The research team tested 45 different NAND flash chips based on 72 to 25 nm technology from six different vendors. The test revealed that the write speed of the pages in a flash block part suffered from dramatic but predictable variations in latency. Error rates also varied significantly when the NAND circuits became worn out. Naturally, SLC came out on top in the tests while MLC was worse and especially TLC NAND worse still.
Then they extrapolated their findings until 2024 when NAND flash is estimated to have come down to 6.5 nanometers. By then the latencies will likely have doubled for MLC flash and increased by a factor of 2.5 for TLC. Error rates are also increased to a level three times higher than today.
