3 ms·

> they are selling us crap. You can completely rewrite a modern 4TB 3D TLC NAND every day for 3 years (3000 TBW). How is that crap? Who even has such needs? Y

> they are selling us crap. You can completely rewrite a modern 4TB 3D TLC NAND every day for 3 years (3000 TBW). How is that crap? Who even has such needs? You are talking about some arbitrary "quality" - I want to be able to rewrite it a zillion times - which make no sense for 99.9% of use cases. I'd much rather have a 4 TB drive which can be rewritten 1000 times versus a same price 256 GB one which can be rewritten 1 million times.

drtgh 3y ago
>You can completely rewrite a modern [..] 3D NAND has introduced degradation when is read data from the disk. You need to calculate then how many times the disk is read, the unwritten free space that will be consumed for to maintain the data when the disk is read, and so on.
- _zoltan_ 3y ago
  and? the TBW guarantees are known in advance.
  - drtgh 3y ago
    The TBW of the disk shown in the specifications is the estimated write limit of each cell multiplied by the number of cells. They don't take into account that in order to read the data of each cell, the adjacent cells will be written and will consume little by little these estimated write limits. Therefore, if you fill the disk and only read data, it will sooner or later go into protection mode or lose data because of it. They could only guarantee the TBW if more memory were added for to cover the writes consumption by the reads usage of the current 3D NAND design. I no longer know how to explain that it is programmed obsolescence, self-destructing disks by read data. We stopped seeing 10 years guaranties when 3D NAND was introduced, so they know well what they are doing.
    - fomine3 3y ago
      I don't think so https://www.jedec.org/standards-documents/focus/flash/solid-state-drives https://www.jedec.org/standards-documents/focus/flash/solid-...
      - drtgh 3y ago
        Why do you link an Industrial SSD Storage standard with write test? It only shows the cells have the corresponding write limits at beginning. My last comment, I'm sorry but I can't spend any more time with this. To read data consume writes, https://dl.acm.org/doi/10.1145/3445814.3446733 https://dl.acm.org/doi/10.1145/3445814.3446733 " 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." Data retention consume writes, https://ghose.cs.illinois.edu/papers/18sigmetrics_3dflash.pdf https://ghose.cs.illinois.edu/papers/18sigmetrics_3dflash.pd... " 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. " Free way.
markhahn 3y ago
TLC is a decent spot, which is why it's still being produced. QLC is less so, since its endurance is only ~300 cycles. there's plenty of tension in the storage industry about this, with vendors saying "don't worry be happy", and purchasers saying "wait, what read:write ratio are you assuming, and how much dedupe?" PLC (probably <100 cycles) is very dubious, IMO, simply because it would only be suitable for very cold data - and at that point you're competing with magnetic media (which has been scaling quite nicely).
- dist-epoch 3y ago
  I have hard drives which I only write to once - long term archive. I will gladly change them fro QLC/PLC storage if price is reasonable. There is a market for any cycle count, it just needs to be reliable and respect the spec.
  - markhahn 3y ago
    that's the tape market I mentioned. agreed, tape doesn't fit the personal market, but it totally dominates anywhere that has scale. the question is: what counts as reliable? if PLC is good for 50 erasures, are you really comfortable with that? it's going to cost more than half of QLC, I assure you... the interesting thing about flash is that people want to use the speed. which means they put in places that have a high content-mutation rate. if it's just personal stuff - mostly cold, little mutation - that's fine but not the main market.
    - dist-epoch 3y ago
      There is a market for high speed read only data - S3 serving, and all kinds of mostly read database scenarios (OLAP). You can have tiered storage, data is first consolidated/updated on TLC drives, and as it ages is moved to PLC storage. RocksDB already supports something like this.
- fomine3 3y ago
  2D TLC wasn't quite decent, but 3D TLC is decent. I think some bad reputation about TLC is come from 2D TLC.

drtgh 3y ago

>You can completely rewrite a modern [..] 3D NAND has introduced degradation when is read data from the disk. You need to calculate then how many times the disk is read, the unwritten free space that will be consumed for to maintain the data when the disk is read, and so on.

_zoltan_ 3y ago
and? the TBW guarantees are known in advance.
- drtgh 3y ago
  The TBW of the disk shown in the specifications is the estimated write limit of each cell multiplied by the number of cells. They don't take into account that in order to read the data of each cell, the adjacent cells will be written and will consume little by little these estimated write limits. Therefore, if you fill the disk and only read data, it will sooner or later go into protection mode or lose data because of it. They could only guarantee the TBW if more memory were added for to cover the writes consumption by the reads usage of the current 3D NAND design. I no longer know how to explain that it is programmed obsolescence, self-destructing disks by read data. We stopped seeing 10 years guaranties when 3D NAND was introduced, so they know well what they are doing.
  - fomine3 3y ago
    I don't think so https://www.jedec.org/standards-documents/focus/flash/solid-state-drives https://www.jedec.org/standards-documents/focus/flash/solid-...
    - drtgh 3y ago
      Why do you link an Industrial SSD Storage standard with write test? It only shows the cells have the corresponding write limits at beginning. My last comment, I'm sorry but I can't spend any more time with this. To read data consume writes, https://dl.acm.org/doi/10.1145/3445814.3446733 https://dl.acm.org/doi/10.1145/3445814.3446733 " 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." Data retention consume writes, https://ghose.cs.illinois.edu/papers/18sigmetrics_3dflash.pdf https://ghose.cs.illinois.edu/papers/18sigmetrics_3dflash.pd... " 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. " Free way.

markhahn 3y ago

TLC is a decent spot, which is why it's still being produced. QLC is less so, since its endurance is only ~300 cycles. there's plenty of tension in the storage industry about this, with vendors saying "don't worry be happy", and purchasers saying "wait, what read:write ratio are you assuming, and how much dedupe?" PLC (probably <100 cycles) is very dubious, IMO, simply because it would only be suitable for very cold data - and at that point you're competing with magnetic media (which has been scaling quite nicely).

dist-epoch 3y ago
I have hard drives which I only write to once - long term archive. I will gladly change them fro QLC/PLC storage if price is reasonable. There is a market for any cycle count, it just needs to be reliable and respect the spec.
- markhahn 3y ago
  that's the tape market I mentioned. agreed, tape doesn't fit the personal market, but it totally dominates anywhere that has scale. the question is: what counts as reliable? if PLC is good for 50 erasures, are you really comfortable with that? it's going to cost more than half of QLC, I assure you... the interesting thing about flash is that people want to use the speed. which means they put in places that have a high content-mutation rate. if it's just personal stuff - mostly cold, little mutation - that's fine but not the main market.
  - dist-epoch 3y ago
    There is a market for high speed read only data - S3 serving, and all kinds of mostly read database scenarios (OLAP). You can have tiered storage, data is first consolidated/updated on TLC drives, and as it ages is moved to PLC storage. RocksDB already supports something like this.
fomine3 3y ago
2D TLC wasn't quite decent, but 3D TLC is decent. I think some bad reputation about TLC is come from 2D TLC.