The Longevity Of Three-Bit-Per-Cell NAND
Q. Does Samsung intend to branch out into peripherals in addition to their storage products? Also, with regards to system memory...what are your thoughts on DDR4 vs. HMC? Obviously you probably can't give details, however, are both types of memory being investigated by Samsung?
A. The area where my division focuses on is OEM SSD offerings where our customers take our SSDs and put them into their product offerings which are then sold to end-users. Our division is more focused on enabling our customers to add value on top of our SSD. With that being said, we have not had any announcements around peripherals using SSDs for our division. Regarding HMC & DDR, my expertise is more focused on SSDs and not on the RAM side. If you are interested in me forwarding to our retail division, please send me your question to: email@example.com and I will forward your question to the retail team.
Q. I’ve seen several tests done by review sites that mention that there is no fear of longevity issues when it comes to TLC NAND with Samsung’s great controller/flash technologies and the 840 EVO looks like a great drive that I want to order. What your personal experience is with this newer nand tech and if we will be seeing the 840 EVO in early August?
A. Samsung was first to successfully deploy 3-bit MLC technology into SSDs. There are three main characteristics that go into determining the "longevity" of a SSD: The type of NAND used, the write workload type and amount, and the capacity of the drive. So, as you see, the type of NAND (e.g., 2-bit MLC, 3-bit MLC) is only one piece of the puzzle when determining what the longevity will be.
3-bit MLC has not always been an option for SSDs but the timing is right to make the switch. Two things have made this possible: the capacity points of SSDs have increased to levels that make the longevity a non-issue and the controller/DSP technology that reads/writes to the NAND Flash has improved each year. For example, if you have a given amount of writes you can do to the NAND Flash itself, and you go from 64GB to 128GB, you double the amount of overall writes (GB's) you can do over the life of the drive. When you go from 128GB to 256GB, you double it again. If we were still using 64GB drives today, 3-bit MLC would likely not be an optimal solution for a 40GB/day workload. However, because we have moved to higher capacities, we have doubled and quadrupled the amount of writes possible to the SSD that weren't possible at smaller capacity points.
We have done tests using typical PC workloads (PCMark) to simulate 40GB's of writes per day on a 256GB 3-bit MLC SSD and have shown it to reach the specified limits of the NAND in 13.5 years; This is a long time in the life of technology. Hard drives were roughly 20GB thirteen years ago. Furthermore, some reviewers have shown that the 3-bit SSDs they have tested can handle much more writes than this. If you move to 2-bit MLC, you can bump this up to over 47 years. The question is: do you really need more than 13 years of writing 40GB's per day? If the answer is yes, then perhaps 2-bit MLC is for you. But, in reality, most people do not write 40GB's every day to their drive and do that for 13 years. And, it is likely the user would have already replaced their entire computer within that 13 years.