5 ms·

There are still new SSDs that use TLC, such as the Silicon Power UD90 (I have one in my system). Not only that, some of them will run in SLC mode when writing n

There are still new SSDs that use TLC, such as the Silicon Power UD90 (I have one in my system). Not only that, some of them will run in SLC mode when writing new data and then move the data to TLC later - advertised as SLC Caching - which could be even better than always-TLC drives (even ones with a DRAM cache).

drtgh 2y ago
Your comment, along with other users, suggests that TLC is a positive attribute for consumers, however, the transition from SLC and MLC NAND to TLC and QLC 3D-NAND actually marked a decline in the longevity of SSDs. Using a mode other than SLC with current SSDs is insane due to the difference with planar NAND features, as the current 3D-NAND consumes writes for everything. 3D-NAND, To read data consume writes [0], " Figure 1a plots the average SSD lifetime consumed by the read-only workloads across 200 days on three SSDs (the detailed parameters of these SSDs can be found from SSD-A/-B/-C in Table 1). As shown in the figure, the lifetime consumed by the read (disturbance) induced writes increases significantly as the SSD density increases. In addition, increasing the read throughput (from 17MBps to 56/68MBps) can greatly accelerate the lifetime consumption. Even more problematically, as the density increases, the SSD lifetime (plotted in Figure 1b) decreases. In addition, SSD-aware write-reduction-oriented system software is no longer sufficient for high-density 3D SSDs, to reduce lifetime consumption. This is because the SSDs entered an era where one can wear out an SSD by simply reading it." 3D-NAND, Data retention consume writes [1], " 3D NAND flash memory exhibits three new error sources that were not previously observed in planar NAND flash memory: (1) layer-to-layer process variation, a new phenomenon specific to the 3D nature of the device, where the average error rate of each 3D-stacked layer in a chip is significantly different; (2) early retention loss, a new phenomenon where the number of errors due to charge leakage increases quickly within several hours after programming; and (3) retention interference, a new phenomenon where the rate at which charge leaks from a flash cell is dependent on the data value stored in the neighboring cell. " [0] https://dl.acm.org/doi/10.1145/3445814.3446733 https://dl.acm.org/doi/10.1145/3445814.3446733 [1] https://ghose.cs.illinois.edu/papers/18sigmetrics_3dflash.pdf https://ghose.cs.illinois.edu/papers/18sigmetrics_3dflash.pd...
- jsheard 2y ago
  Even datacenter-grade drives scarcely use SLC or MLC anymore since TLC has matured to the point of being more than good enough even in most server workloads, what possible need would 99% of consumers have for SLC/MLC nowadays? If you really want a modern SLC drive there's the Kioxia FL6, which has a whopping 350,400 TB of write endurance in the 3TB variant, but it'll cost you $4320. Alternatively you can get 4TB of TLC for $300 and take your chances with "only" 2400 TB endurance.
  - drtgh 2y ago
    TLC cannot mature as long as it continues to use 3D-NAND without utilizing a more advanced material science. Reading data and preserving data consume writes, what degrades the memory, because the traces in the vertical stack of the circuit create interference. Perhaps there are techniques available to separate the traces, but this would ultimately increase the surface area? which seems to be something they are trying to avoid. You should not use datacenter SSD disks as a reference, as they typically do not last more than two years and a half. It appears to be a profitable opportunity for the SSD manufacturer, and increasing longevity does not seem to be a priority. To be more specific, we are talking about planned obsolescence for consumer and enterprise SSD disks. > If you really want a modern SLC drive there's the Kioxia FL6, which has a whopping 350,400 TB of write endurance in the 3TB variant, but it'll cost you $4320. Did you read the OP article?
  - LoganDark 2y ago
    I got 4TB of TLC for $230 (Silicon Power UD90). It even has SLC caching (can use parts of the flash in SLC mode for short periods of time).
    - jsheard 2y ago
      True, I was looking at the prices for higher end drives with on-board DRAM, but DRAM-less drives like that UD90 are also fine in the age of NVMe. Going DRAM-less was a significant compromise on SATA SSDs, but NVMe allows the drive to borrow a small chunk of system RAM over PCIe DMA, and in practice that works well enough. (Caveat: that DMA trick doesn't work if you put the drive in a USB enclosure, so if that's your use-case you should ideally still look for a drive with its own DRAM)

drtgh 2y ago

Your comment, along with other users, suggests that TLC is a positive attribute for consumers, however, the transition from SLC and MLC NAND to TLC and QLC 3D-NAND actually marked a decline in the longevity of SSDs. Using a mode other than SLC with current SSDs is insane due to the difference with planar NAND features, as the current 3D-NAND consumes writes for everything. 3D-NAND, To read data consume writes [0], " Figure 1a plots the average SSD lifetime consumed by the read-only workloads across 200 days on three SSDs (the detailed parameters of these SSDs can be found from SSD-A/-B/-C in Table 1). As shown in the figure, the lifetime consumed by the read (disturbance) induced writes increases significantly as the SSD density increases. In addition, increasing the read throughput (from 17MBps to 56/68MBps) can greatly accelerate the lifetime consumption. Even more problematically, as the density increases, the SSD lifetime (plotted in Figure 1b) decreases. In addition, SSD-aware write-reduction-oriented system software is no longer sufficient for high-density 3D SSDs, to reduce lifetime consumption. This is because the SSDs entered an era where one can wear out an SSD by simply reading it." 3D-NAND, Data retention consume writes [1], " 3D NAND flash memory exhibits three new error sources that were not previously observed in planar NAND flash memory: (1) layer-to-layer process variation, a new phenomenon specific to the 3D nature of the device, where the average error rate of each 3D-stacked layer in a chip is significantly different; (2) early retention loss, a new phenomenon where the number of errors due to charge leakage increases quickly within several hours after programming; and (3) retention interference, a new phenomenon where the rate at which charge leaks from a flash cell is dependent on the data value stored in the neighboring cell. " [0] https://dl.acm.org/doi/10.1145/3445814.3446733 https://dl.acm.org/doi/10.1145/3445814.3446733 [1] https://ghose.cs.illinois.edu/papers/18sigmetrics_3dflash.pdf https://ghose.cs.illinois.edu/papers/18sigmetrics_3dflash.pd...

jsheard 2y ago
Even datacenter-grade drives scarcely use SLC or MLC anymore since TLC has matured to the point of being more than good enough even in most server workloads, what possible need would 99% of consumers have for SLC/MLC nowadays? If you really want a modern SLC drive there's the Kioxia FL6, which has a whopping 350,400 TB of write endurance in the 3TB variant, but it'll cost you $4320. Alternatively you can get 4TB of TLC for $300 and take your chances with "only" 2400 TB endurance.
- drtgh 2y ago
  TLC cannot mature as long as it continues to use 3D-NAND without utilizing a more advanced material science. Reading data and preserving data consume writes, what degrades the memory, because the traces in the vertical stack of the circuit create interference. Perhaps there are techniques available to separate the traces, but this would ultimately increase the surface area? which seems to be something they are trying to avoid. You should not use datacenter SSD disks as a reference, as they typically do not last more than two years and a half. It appears to be a profitable opportunity for the SSD manufacturer, and increasing longevity does not seem to be a priority. To be more specific, we are talking about planned obsolescence for consumer and enterprise SSD disks. > If you really want a modern SLC drive there's the Kioxia FL6, which has a whopping 350,400 TB of write endurance in the 3TB variant, but it'll cost you $4320. Did you read the OP article?
- LoganDark 2y ago
  I got 4TB of TLC for $230 (Silicon Power UD90). It even has SLC caching (can use parts of the flash in SLC mode for short periods of time).
  - jsheard 2y ago
    True, I was looking at the prices for higher end drives with on-board DRAM, but DRAM-less drives like that UD90 are also fine in the age of NVMe. Going DRAM-less was a significant compromise on SATA SSDs, but NVMe allows the drive to borrow a small chunk of system RAM over PCIe DMA, and in practice that works well enough. (Caveat: that DMA trick doesn't work if you put the drive in a USB enclosure, so if that's your use-case you should ideally still look for a drive with its own DRAM)