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> Flash has to be powered so the contents of each cell can be refreshed so data isn't lost That's not how flash storage works. You can unplug a flash drive and

> Flash has to be powered so the contents of each cell can be refreshed so data isn't lost That's not how flash storage works. You can unplug a flash drive and put it on a shelf and it will keep its data. Here's a review of portable, external SSDs that don't lose their data when not plugged in: * https://www.tomshardware.com/reviews/best-external-hard-drive-ssd,5987.html https://www.tomshardware.com/reviews/best-external-hard-driv... Are you thinking of DRAM perhaps?

nisegami 5y ago
No, they're referring to bit rot on flash storage due to slow leakage of the charge that represents the data. It occurs on long time scales, definitely years. But the more bits per cell (SLC vs TLC vs QLC), the more likely it is.
- deleted 5y ago
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- throw0101a 5y ago
  > No, they're referring to bit rot on flash storage due to slow leakage of the charge that represents the data. Could not the same be said of the magnetism of the bits on spinning rust? What's the shelf life of data on an HDD? Tapes also have magnetic charge, but are designed to be "unrefreshed" for longer periods of time.
  - labawi 5y ago
    Tapes and HDDs are magnetic. Flash and DRAM is electric. It is easier to create magnetically stable structures (magnets) than non-leaking capacitors. Flash has a better insulator than DRAM, but it wears out with use and leaks more with higher temperature, densities, less margin with more bits per cell...
JaimeThompson 5y ago
Depending on the design of the flash, the storage temperature, and other factors that data can rot. Please see [1] for one source. [1] https://www.ibm.com/support/pages/flash-data-retention-0 https://www.ibm.com/support/pages/flash-data-retention-0
AshamedCaptain 5y ago
I remember there was some analysis done on the SSD of an old early model Surface Pro showing that with age the SSD would become slower at _reading_ data that had not been modified recently. EDIT: It was this story https://mspoweruser.com/samsung-releases-firmware-update-for-its-ssds-in-surface-pro-3-devices-to-improve-performance/ https://mspoweruser.com/samsung-releases-firmware-update-for... The fact that the SSD controller has to do anything at all to read data that was stored only a year ago is a hint that data retention on a SSD requires some (powered) effort.
- wtallis 5y ago
  Slower read speeds on old data is indeed a symptom of the SSD controller having to use its slower and more thorough error-correction mechanisms to recover data. However, since the first few generations of Microsoft Surface machines, the SSD market has made several relevant changes: - a switch from storing charge in a conductive floating gate structure to storing charge in a non-conductive charge trap layer (Intel's flash is the one holdout here) - a switch from planar to 3D fabrication, allowing a huge one-time increase in memory cell volume and thus the number of electrons used to represent each bit, and also opening up avenues of scaling capacity that don't require reducing cell volume - dedicating far more transistors to error correction in SSD controllers, greatly reducing the performance impact of correctable bit errors but also enabling the use of more robust error correction codes

nisegami 5y ago

No, they're referring to bit rot on flash storage due to slow leakage of the charge that represents the data. It occurs on long time scales, definitely years. But the more bits per cell (SLC vs TLC vs QLC), the more likely it is.

deleted 5y ago
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throw0101a 5y ago
> No, they're referring to bit rot on flash storage due to slow leakage of the charge that represents the data. Could not the same be said of the magnetism of the bits on spinning rust? What's the shelf life of data on an HDD? Tapes also have magnetic charge, but are designed to be "unrefreshed" for longer periods of time.
- labawi 5y ago
  Tapes and HDDs are magnetic. Flash and DRAM is electric. It is easier to create magnetically stable structures (magnets) than non-leaking capacitors. Flash has a better insulator than DRAM, but it wears out with use and leaks more with higher temperature, densities, less margin with more bits per cell...

JaimeThompson 5y ago

Depending on the design of the flash, the storage temperature, and other factors that data can rot. Please see [1] for one source. [1] https://www.ibm.com/support/pages/flash-data-retention-0 https://www.ibm.com/support/pages/flash-data-retention-0

AshamedCaptain 5y ago

I remember there was some analysis done on the SSD of an old early model Surface Pro showing that with age the SSD would become slower at _reading_ data that had not been modified recently. EDIT: It was this story https://mspoweruser.com/samsung-releases-firmware-update-for-its-ssds-in-surface-pro-3-devices-to-improve-performance/ https://mspoweruser.com/samsung-releases-firmware-update-for... The fact that the SSD controller has to do anything at all to read data that was stored only a year ago is a hint that data retention on a SSD requires some (powered) effort.

wtallis 5y ago
Slower read speeds on old data is indeed a symptom of the SSD controller having to use its slower and more thorough error-correction mechanisms to recover data. However, since the first few generations of Microsoft Surface machines, the SSD market has made several relevant changes: - a switch from storing charge in a conductive floating gate structure to storing charge in a non-conductive charge trap layer (Intel's flash is the one holdout here) - a switch from planar to 3D fabrication, allowing a huge one-time increase in memory cell volume and thus the number of electrons used to represent each bit, and also opening up avenues of scaling capacity that don't require reducing cell volume - dedicating far more transistors to error correction in SSD controllers, greatly reducing the performance impact of correctable bit errors but also enabling the use of more robust error correction codes