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Comment by LoganDark

2 years ago

> Your comment, along with other users, suggests that TLC is a positive attribute for consumers

TLC is better than QLC, which is specifically what my comment was addressing; I never implied that it's better than SLC though, so just don't, please.

It's interesting to see that 3D-NAND has other issues even when run in SLC mode, though.

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LoganDark

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drtgh  2 years ago

> I never implied that it's better than SLC though, so just don't, please.

My apologies.

> It's interesting to see that 3D-NAND has other issues even when run in SLC mode, though.

Basically the SSD manufacturers are increasing capacity by adding more layers (3D-NAND). When one cell is read in the vertical stack, the interferences produced by the traces in the area increases the cells that need to be rewritten, what consumes the life of the device, by design.

  • wtallis  2 years ago

    > When one cell is read in the vertical stack, the interferences produced by the traces in the area increases the cells that need to be rewritten, what consumes the life of the device, by design.

    You should try being honest about the magnitude of this effect. It takes thousands of read operations at a minimum to cause a read disturb that can be fixed with one write. What you're complaining about is the NAND equivalent of DRAM rowhammer. It's not a serious problem in practice.

    • drtgh  2 years ago

      Not NAND equivalent as the larger the stack, the larger the writings on the continuous cells, not just rewriting a single cell.

      Here, the dishonest are the SSD manufacturers of the last decade, and they are feeling so comfortable as to introduce QLC into the market.

      > It's not a serious problem in practice.

      It's as serious as in to read data consume the disk, and the faster its read the faster it's consumed [0]. You should have noticed that SSD disks no longer come with a 10-year warranty.

          "under low throughput read-only workloads, SSD-A/-B/-C/-D/-E/-F extensively rewrite the potentially-disturbed data in the background, to mitigate the read (disturbance) induced latency problem and sustain a good read performance. Such rewrites significantly consume the already-reduced SSD lifetime. "

      Under low throughput read-only workloads.

      It is a paper from 2021, what means sci-hub can be used to read it.

      [0] https://dl.acm.org/doi/10.1145/3445814.3446733

      7 replies →

  • LoganDark  2 years ago

    > When one cell is read in the vertical stack, the interferences produced by the traces in the area increases the cells that need to be rewritten, what consumes the life of the device

    So 3D-NAND suffers interference between the stacked layers? (Introducing Columnhammer... /s)