Changes to Data Center Flash
Over the past six years, Data Center Flash has moved rapidly from SLC Flash which stores one data bit per memory cell through MLC flash storing two bits per cell. It will then go to the current three-bit TLC Flash, which now accounts for over 90% of all flash shipments. Each move lowered the per-GB cost of flash but also delivered diminishing price reductions. This was done while introducing increasing technical challenges maintaining flash performance, reliability, and write-life.
Compared with TLC, QLC stores 33% more data per memory cell, but that does not make QLC flash drives or modules one-third cheaper. Due to the costs incurred, compensating for QLC’s lower quality, the first QLC drives that shipped last year were closer to 10% cheaper. As the technology develops, the price gap is expected to widen, but the long-term prospects for QLC are not as strong as they were for TLC. That is not only because of the diminishing returns from bit-count increases, but also because the introduction of TLC coincided with an industry move from 2-D to 3-D physical flash chips. That change in physical structure significantly offset the lower quality of TLC Flash and helped it replace MLC Flash. This time around, there is no such parallel development to help QLC replace TLC.
Forecasting in Data Centers
Nevertheless, there are forecasts that QLC will see significant usage in Data Centers. At one end of the spectrum, an executive at a very large chip maker confidently told 451 Research last year that QLC will repeat history by becoming the new TLC. Western Digital has publicly predicted that QLC will account for only about half of all flash capacity shipments by 2025.
Similarly, Pure Storage says it does not expect QLC to fully replace TLC at any time in the near- or even midterm future, and perhaps never. But it projects that QLC will allow flash to displace yet more disk. Among Pure’s major competitors, one has said privately that it will adopt QLC in its Data Center storage systems within the next few months, but others have said that, at present, the new flash variant is not yet cheap enough to justify the move.