4 ms·

It's QLC NAND (~1000 program/erase cycles from https://www.purestorage.com/knowledge/what-is-qlc-flash.html https://www.purestorage.com/knowledge/what-is-qlc-fl

by canucker2016 3y ago

It's QLC NAND (~1000 program/erase cycles from https://www.purestorage.com/knowledge/what-is-qlc-flash.html https://www.purestorage.com/knowledge/what-is-qlc-flash.html). eesh. [Update] from https://www.anandtech.com/show/20007/samsung-teases-256-tb-ssd-3d-qlc-nand-at-its-best https://www.anandtech.com/show/20007/samsung-teases-256-tb-s...: "Samsung's 256 TB SSD is based on 3D QLC NAND memory and probably uses innovative packaging to cram multiple 3D QLC NAND devices into stacks." 3D QLC should have higher endurance than regular QLC. We'll have to wait and see for the spec sheet.

sebazzz 3y ago
> The PM9D3a achieves a mean time between failure (MTBF) of 2.5Mhr, a 25% improvement over the previous generation, allowing customers to operate more stable services. This number doesn't reflect that, but maybe the MTBF is just a distraction.
- wtallis 3y ago
  Yes, MTBF as reported on the spec sheets is purely a distraction when it comes to SSD reliability.
earthscienceman 3y ago
It is very eesh. But tbf, I would precisely use this for single-drive monthly cold storage backups of a large raid nas for example.
- rasz 3y ago
  NAND doesnt work for cold storage. https://www.ibm.com/support/pages/node/6382908 https://www.ibm.com/support/pages/node/6382908 > The JEDEC spec for Enterprise SSD drives requires that the drives retain data for a minimum of 3 months at 40C >A system (and its enclosed drives) should be powered up at least 2 weeks after 2 months of system power off.
  - wtallis 3y ago
    The bit that everyone likes to leave out about the 3 months at 40C retention standard is that it applies to drives at end of life, with all their rates write endurance used up. Drives that are not so worn-out have much longer retention—and a drive used only for cold storage of infrequent backups would hardly use any of its write endurance. The recommendation to have the drive be powered up for two weeks after taking it out of cold storage is only so that the drive can do it's low-priority background checks of data integrity. If you do a full scrub of your data from the host system, you don't need to worry about that, because you'll be giving the drive all the same opportunities to discover bitrot. None of the above changes the fact that SSDs are still quite expensive for cold storage purposes.
drtgh 3y ago
• 4-bit per cell = QLC ······ 1'000 write cycles per cell • 3-bit per cell = TLC ······· 3'000 write cycles per cell • 2-bit per cell = MLC ····· 10'000 write cycles per cell • 2-bit per cell = eMLC ··· 30'000 write cycles per cell • 1-bit per cell = SLC ··· 100'000 write cycles per cell The above degradation cycles are optimist. Looks like the SSD technology is not evolving, but counter-evolving in terms of data integrity; there are neither MLC, eMLC nor SLC disk nowadays (seven years ago widely available).
- wtallis 3y ago
  > Looks like the SSD technology is not evolving, but counter-evolving in terms of data integrity; there are neither MLC, eMLC nor SLC disk nowadays (seven years ago widely available). Some of this is from more advanced SSD controllers with more robust error correction, enabling drives to get better uncorrectable bit error rates out of flash with a higher raw bit error rate. But most of this is because SLC and MLC simply had more write endurance than people needed, and sacrificing endurance to get higher capacity made for more useful drives. And as larger SSDs have become more affordable, SSDs have been taking over more use cases from hard drives, so unlike a decade ago SSDs aren't just for frequently-modified hot data any more—you don't need as many P/E cycles or DWPD when most of your data isn't changing very often.
  - drtgh 3y ago
    I think they crossed the limit of sacrifice that is understandable given the endurance of the materials currently used in NAND. Cell modes are done by charging a cell to a level on write, and measuring the voltage on read. The more bits per cell, the more voltage divisions, and the sooner these voltages divisions turns unreadable, while the material degrades. Technically is on the manufacturer's firmware to decide what cell mode is going to use the NAND, assuming the hardware allows it (ADC/DAC, etc). But even if the data is not changing very often, the controller of the disk needs to do internal writes for to refresh the cell, or even change the data of cell, in order to avoid data loss. So IMHO, they are not giving more capacity, due that capacity is going to be consumed for to try to keep alive the data. If one fills the QLC disk of the article for long term storage, bad things will happen, as I understand it. May be should be the user who decide what bit mode must use the disk. But what is happening, I think, is along years they are stretching like chewing gum the NAND incrementing the bits by cell, hopping the people adopt the reduced endurance as a normality at prices of data-stored, not of NAND chips-used, at time they limit their chips production.

sebazzz 3y ago

> The PM9D3a achieves a mean time between failure (MTBF) of 2.5Mhr, a 25% improvement over the previous generation, allowing customers to operate more stable services. This number doesn't reflect that, but maybe the MTBF is just a distraction.

wtallis 3y ago
Yes, MTBF as reported on the spec sheets is purely a distraction when it comes to SSD reliability.

earthscienceman 3y ago

It is very eesh. But tbf, I would precisely use this for single-drive monthly cold storage backups of a large raid nas for example.

rasz 3y ago
NAND doesnt work for cold storage. https://www.ibm.com/support/pages/node/6382908 https://www.ibm.com/support/pages/node/6382908 > The JEDEC spec for Enterprise SSD drives requires that the drives retain data for a minimum of 3 months at 40C >A system (and its enclosed drives) should be powered up at least 2 weeks after 2 months of system power off.
- wtallis 3y ago
  The bit that everyone likes to leave out about the 3 months at 40C retention standard is that it applies to drives at end of life, with all their rates write endurance used up. Drives that are not so worn-out have much longer retention—and a drive used only for cold storage of infrequent backups would hardly use any of its write endurance. The recommendation to have the drive be powered up for two weeks after taking it out of cold storage is only so that the drive can do it's low-priority background checks of data integrity. If you do a full scrub of your data from the host system, you don't need to worry about that, because you'll be giving the drive all the same opportunities to discover bitrot. None of the above changes the fact that SSDs are still quite expensive for cold storage purposes.

drtgh 3y ago

• 4-bit per cell = QLC ······ 1'000 write cycles per cell • 3-bit per cell = TLC ······· 3'000 write cycles per cell • 2-bit per cell = MLC ····· 10'000 write cycles per cell • 2-bit per cell = eMLC ··· 30'000 write cycles per cell • 1-bit per cell = SLC ··· 100'000 write cycles per cell The above degradation cycles are optimist. Looks like the SSD technology is not evolving, but counter-evolving in terms of data integrity; there are neither MLC, eMLC nor SLC disk nowadays (seven years ago widely available).

wtallis 3y ago
> Looks like the SSD technology is not evolving, but counter-evolving in terms of data integrity; there are neither MLC, eMLC nor SLC disk nowadays (seven years ago widely available). Some of this is from more advanced SSD controllers with more robust error correction, enabling drives to get better uncorrectable bit error rates out of flash with a higher raw bit error rate. But most of this is because SLC and MLC simply had more write endurance than people needed, and sacrificing endurance to get higher capacity made for more useful drives. And as larger SSDs have become more affordable, SSDs have been taking over more use cases from hard drives, so unlike a decade ago SSDs aren't just for frequently-modified hot data any more—you don't need as many P/E cycles or DWPD when most of your data isn't changing very often.
- drtgh 3y ago
  I think they crossed the limit of sacrifice that is understandable given the endurance of the materials currently used in NAND. Cell modes are done by charging a cell to a level on write, and measuring the voltage on read. The more bits per cell, the more voltage divisions, and the sooner these voltages divisions turns unreadable, while the material degrades. Technically is on the manufacturer's firmware to decide what cell mode is going to use the NAND, assuming the hardware allows it (ADC/DAC, etc). But even if the data is not changing very often, the controller of the disk needs to do internal writes for to refresh the cell, or even change the data of cell, in order to avoid data loss. So IMHO, they are not giving more capacity, due that capacity is going to be consumed for to try to keep alive the data. If one fills the QLC disk of the article for long term storage, bad things will happen, as I understand it. May be should be the user who decide what bit mode must use the disk. But what is happening, I think, is along years they are stretching like chewing gum the NAND incrementing the bits by cell, hopping the people adopt the reduced endurance as a normality at prices of data-stored, not of NAND chips-used, at time they limit their chips production.