3 ms·

Very disturbing, the article talks about the number of bits to be read per cell like if it were only a matter of speed. In addition to your comment (related),

by drtgh 1y ago

Very disturbing, the article talks about the number of bits to be read per cell like if it were only a matter of speed. In addition to your comment (related), when 3D-NAND cells are read, interference by the traces (charge-trap disturbs) requires the neighbour cells to be refreshed with writes, if the controller wants to conserve data integrity. This did not happen with 2D-NAND in the past. Reading data from one cell in 3D-NAND involves writing cells; reading data in 3D-NAND consumes disk endurance. (Not to mention, temperature/number of layers/endurance)

zozbot234 1y ago
The read disturb effect happens with 2D-NAND, it's just rare.
pkaye 1y ago
I used to work in SSD controller firmware. This kind of issue existed more than 10 years ago. To achieve higher capacity with each generation of NAND you are trading off everything else (endurance, retention, read/program times, etc) little by little. 20 years ago it was so rare to see any kind of errors with SLC NAND that error detection and handling was fairly simple.
- userbinator 1y ago
  I have some small USB drives from that era with SLC rated for 10 years of retention after 100k cycles, meaning a 64MB drive has a total endurance of 6.4TB. True binary capacity too, with no wear leveling either, as only the spares on each page were needed for a simple ECC. Too bad planned obsolescence got in the way, or we would've ended up today with bigger SLC drives that are fast and simple and just as reliable.
  - Dylan16807 1y ago
    There's no planned obsolescence for my use case. I've never done enough writes to wear out an SSD. While I might buy an SLC flash drive if it was properly available, for internal drives TLC has barely any downsides. I very rarely get limited to 500MB/s, I need to turn it on sometimes, and I get 2.8x the space. Sounds great.
    - userbinator 1y ago
      You may find this interesting (or horrifying): https://news.ycombinator.com/item?id=43739028 https://news.ycombinator.com/item?id=43739028 tl;dr: worn flash shows severe degradation, but more worrying is that there are even signs of retention failure with TLC flash that has been programmed only once.
      - Dylan16807 1y ago
        Worrying if you want to leave it unpowered. I made that an explicit part of the tradeoff. I don't value that feature very much, and I don't think many other people value it much either. It's important to make people aware of that problem, but they can solve it in other ways. I'd pay an extra $20 to upgrade a 0.25TB flash drive to SLC and get unlimited retention. For a drive in my computer, I don't need it and it would cost far more. Edit: I could even get an extra hard drive just to act as a backup, and TLC+HDD would still be half the price of SLC.
  - zozbot234 1y ago
    Good TLC/QLC drives will likely store your data as SLC if you overprovision them badly enough. (I.e. use only one fourth or less of the rated storage, since QLC stores four bits per cell. You can sort of verify this via benchmarking, since the SLC "mode" has far better performance overall.)

by drtgh 1y ago

zozbot234 1y ago

The read disturb effect happens with 2D-NAND, it's just rare.

pkaye 1y ago

I used to work in SSD controller firmware. This kind of issue existed more than 10 years ago. To achieve higher capacity with each generation of NAND you are trading off everything else (endurance, retention, read/program times, etc) little by little. 20 years ago it was so rare to see any kind of errors with SLC NAND that error detection and handling was fairly simple.

userbinator 1y ago
I have some small USB drives from that era with SLC rated for 10 years of retention after 100k cycles, meaning a 64MB drive has a total endurance of 6.4TB. True binary capacity too, with no wear leveling either, as only the spares on each page were needed for a simple ECC. Too bad planned obsolescence got in the way, or we would've ended up today with bigger SLC drives that are fast and simple and just as reliable.
- Dylan16807 1y ago
  There's no planned obsolescence for my use case. I've never done enough writes to wear out an SSD. While I might buy an SLC flash drive if it was properly available, for internal drives TLC has barely any downsides. I very rarely get limited to 500MB/s, I need to turn it on sometimes, and I get 2.8x the space. Sounds great.
  - userbinator 1y ago
    You may find this interesting (or horrifying): https://news.ycombinator.com/item?id=43739028 https://news.ycombinator.com/item?id=43739028 tl;dr: worn flash shows severe degradation, but more worrying is that there are even signs of retention failure with TLC flash that has been programmed only once.
    - Dylan16807 1y ago
      Worrying if you want to leave it unpowered. I made that an explicit part of the tradeoff. I don't value that feature very much, and I don't think many other people value it much either. It's important to make people aware of that problem, but they can solve it in other ways. I'd pay an extra $20 to upgrade a 0.25TB flash drive to SLC and get unlimited retention. For a drive in my computer, I don't need it and it would cost far more. Edit: I could even get an extra hard drive just to act as a backup, and TLC+HDD would still be half the price of SLC.
- zozbot234 1y ago
  Good TLC/QLC drives will likely store your data as SLC if you overprovision them badly enough. (I.e. use only one fourth or less of the rated storage, since QLC stores four bits per cell. You can sort of verify this via benchmarking, since the SLC "mode" has far better performance overall.)