3 ms·

I envy you. All I read there was "write endurance and data retention halved again"

by rasz 4y ago

Dylan16807 4y ago
I have no idea why you'd read that when the cells are the same size as before.
- nousermane 4y ago
  That outcome would be expected from either decreasing cell size, or increasing bits/cell (what used to be commonly called SLC/MLC/TLC/QLC). I don't see TFA mentioning either directly, but there are some hints that one of the two (or both) did happen: Number of layers increased from 176 to 232 (that explains 32% increase) but bits/chip area has doubled (total density increased by 100%). Where does the rest of this increase coming from, you reckon?
  - HeyItsMatt 4y ago
    From a much better Anandtech article: 32% increase in layers, 40% increase in die area. https://www.anandtech.com/show/17509/microns-232-layer-nand-now-shipping https://www.anandtech.com/show/17509/microns-232-layer-nand-... A bunch of the cost is test and packaging which is constant so there will be a small cost per bit reduction. But the new chip will cost significantly more to manufacture than a 512Gbit device. No free lunch.
londons_explore 4y ago
I don't see these as problems as long as software is smart enough. It merely requires the device to be always powered up (read: has a backup battery that can do periodic flash rewrites for 5 years). And it requires the controller to keep track of the current endurance of every page. A 'worn out' page can still hold data, it just holds either less data, or holds that data for fewer hours before needing to be rewritten. Long gone are the days of "you can rewrite this data 100,000 times, and then leave it 10 years and it'll still be there". The new normal is "rewrite this data every 20 days to begin with, and after doing 1000 writes you'll need to rewrite the data every hour, or double the ECC bits and then you'll need to rewrite every day".
- rasz 4y ago
  >or double the ECC bits Are you aware of even a single ssd product allowing user to reconfigure capacity outside of obtaining secret/proprietary non public manufacturer service software? The only technical way for a drive to automagically shrink size on its own is by starting to mark TRIM freed sectors as BAD and hoping OS running on top will be able to recognize this and transfer BAD status to the filesystem - thats a lot of assumptions. No such drive exists either, drives ship with spare capacity and existence of BAD sectors is treated as a catastrophic event signaling running out of backup NAND.
  - consp 4y ago
    On SAS disks you can reduce the capacity. I don't know if this has any influence on spare sectors and write cycles though.
    - rasz 4y ago
      You can reserve space by setting host protected area (HPA). There are even people theorizing this might add provisioning are to an SSD https://www.thomas-krenn.com/en/wiki/SSD_Over-provisioning_using_hdparm https://www.thomas-krenn.com/en/wiki/SSD_Over-provisioning_u... . But so far there is zero evidence for it. HPA is not a magic nobody touches area, its an area reserved for special superuser use and no Drive will simply start reusing it for its own internal processes.
  - londons_explore 4y ago
    Drives internally do this with their reserved sectors. They also reallocate sectors between 'fast access' and 'long term storage', where the long term storage uses larger logical pages and hierarchical ECC, allowing a lower percentage of ECC overhead at the cost of performance. At some point, I wouldn't be surprised if an SSD manufacturer releases a drive with a driver which can reduce the user-visible disk size as it ages. It would probably involve using a 'balloon file', in a similar way to Memory ballooning [1] [1]: https://en.wikipedia.org/wiki/Memory_ballooning https://en.wikipedia.org/wiki/Memory_ballooning
  - 4y ago

I envy you. All I read there was "write endurance and data retention halved again"

by rasz 4y ago

I envy you. All I read there was "write endurance and data retention halved again"

Dylan16807 4y ago

I have no idea why you'd read that when the cells are the same size as before.

nousermane 4y ago
That outcome would be expected from either decreasing cell size, or increasing bits/cell (what used to be commonly called SLC/MLC/TLC/QLC). I don't see TFA mentioning either directly, but there are some hints that one of the two (or both) did happen: Number of layers increased from 176 to 232 (that explains 32% increase) but bits/chip area has doubled (total density increased by 100%). Where does the rest of this increase coming from, you reckon?
- HeyItsMatt 4y ago
  From a much better Anandtech article: 32% increase in layers, 40% increase in die area. https://www.anandtech.com/show/17509/microns-232-layer-nand-now-shipping https://www.anandtech.com/show/17509/microns-232-layer-nand-... A bunch of the cost is test and packaging which is constant so there will be a small cost per bit reduction. But the new chip will cost significantly more to manufacture than a 512Gbit device. No free lunch.

londons_explore 4y ago

I don't see these as problems as long as software is smart enough. It merely requires the device to be always powered up (read: has a backup battery that can do periodic flash rewrites for 5 years). And it requires the controller to keep track of the current endurance of every page. A 'worn out' page can still hold data, it just holds either less data, or holds that data for fewer hours before needing to be rewritten. Long gone are the days of "you can rewrite this data 100,000 times, and then leave it 10 years and it'll still be there". The new normal is "rewrite this data every 20 days to begin with, and after doing 1000 writes you'll need to rewrite the data every hour, or double the ECC bits and then you'll need to rewrite every day".

rasz 4y ago
>or double the ECC bits Are you aware of even a single ssd product allowing user to reconfigure capacity outside of obtaining secret/proprietary non public manufacturer service software? The only technical way for a drive to automagically shrink size on its own is by starting to mark TRIM freed sectors as BAD and hoping OS running on top will be able to recognize this and transfer BAD status to the filesystem - thats a lot of assumptions. No such drive exists either, drives ship with spare capacity and existence of BAD sectors is treated as a catastrophic event signaling running out of backup NAND.
- consp 4y ago
  On SAS disks you can reduce the capacity. I don't know if this has any influence on spare sectors and write cycles though.
  - rasz 4y ago
    You can reserve space by setting host protected area (HPA). There are even people theorizing this might add provisioning are to an SSD https://www.thomas-krenn.com/en/wiki/SSD_Over-provisioning_using_hdparm https://www.thomas-krenn.com/en/wiki/SSD_Over-provisioning_u... . But so far there is zero evidence for it. HPA is not a magic nobody touches area, its an area reserved for special superuser use and no Drive will simply start reusing it for its own internal processes.
- londons_explore 4y ago
  Drives internally do this with their reserved sectors. They also reallocate sectors between 'fast access' and 'long term storage', where the long term storage uses larger logical pages and hierarchical ECC, allowing a lower percentage of ECC overhead at the cost of performance. At some point, I wouldn't be surprised if an SSD manufacturer releases a drive with a driver which can reduce the user-visible disk size as it ages. It would probably involve using a 'balloon file', in a similar way to Memory ballooning [1] [1]: https://en.wikipedia.org/wiki/Memory_ballooning https://en.wikipedia.org/wiki/Memory_ballooning
- 4y ago