4 ms·

Is keeping a SSD powered on enough to prevent bit rot?

MCRed 11y ago
It should have no impact. It really is about write capacity. The little cells can only handle being changed so many times before they wear out. The wearing is a chemical/semi-conductor type problem. It's not like DRAM where keeping power applied keeps the cells "fresh" (and in DRAM it's done literally be refreshing each cell at a certain frequency.) The simple equation is the more times a cell is erased the sooner it fails. Write leveling and other software efforts work to spread around or eliminate unnecessary writes. But over the practical life of a drive (5-10 years?) being powered off will not cause them to lose data. Edit: I've been following FLASH technology since before the terms "FLASH" was coined, back when it was called EEPROM -- Electrically Erasable Programmable Read Only Memory, an evolution of PROMs (write once) and ERPOMS (erasable with UV light). If there's a myth out there that flash drives just forget things, I'd like to point out that I've had flash drives (low quality at that) from the 1990s that were left for 20 years and then read successfully! Show some citations of real evidence before you down vote me.
- cjensen 11y ago
  That's incorrect. Charge leaks very slowly out of cells. It's not a big issue, but it does happen. Powered-on SSD firmware knows about the problem and will maintain the cells. [1] http://www.anandtech.com/show/9248/the-truth-about-ssd-data-retention http://www.anandtech.com/show/9248/the-truth-about-ssd-data-...
  - acqq 11y ago
    And AnandTech quotes Intel materials who often boasts to have the most durable drives. Imagine what happens to other ones.
    - philjohn 11y ago
      Samsung back up the 850 Pro with a 10 year/150TB host writes warranty. The trick is moving back 2 processes, which alleviates some of the issues they've faced with the 840 series.
      - acqq 11y ago
        The warranty is certainly not "it will keep the data 10 years without being powered on." We discuss the topic of how long SSDs retain the data when powered off. Intel says, powered off but stored on just 35 degrees C, only 14 weeks, as published by AnandTech: http://images.anandtech.com/doci/9248/3.PNG http://images.anandtech.com/doci/9248/3.PNG And Intel is proud to be more reliable than others. In one of their presentations I've seen they show that they use some very high tech setups (like accelerators!) to measure the degradations fast, and that the other producers fare worse on their tests.
- deleted 11y ago
  [deleted]
- pgeorgi 11y ago
  > flash drives (low quality at that) from the 1990s 90s flash is more likely NOR, which doesn't suffer some of the failure modes of NAND. As for NAND, micron would probably not discuss rumors about their technology as fact: https://www.micron.com/~/media/Documents/Products/Presentation/flash_mem_summit_jcooke_inconvenient_truths_nand.pdf https://www.micron.com/~/media/Documents/Products/Presentati... (read disturb on page 19, data retention on page 21)
bifrost 11y ago
No need to power or refresh, but if you have a cruddy SSD you should keep other backups.
- ChrisLomont 11y ago
  SSDs should suffer the same bit-rot other flash does. JEDEC specs require that a drive that has used 10% of its rewrite capacity it should hold the data for at least 10 years, and this decreases to when a drive has used 100% of its rewrite capacity it should hold the data for at least one year. So to meet specs a consumer drive should fall in between these timeframes. However, cheaper drives may well not completely meet this spec; this is common for many other manufacturing processes. The bit rot also depends on many other factors, the most important being temperature (you cannot outwit statistical mechanics). The next one is a combination of hot neutrons causing bit flips from impurities in the material and from cosmic rays, the latter of which can be reduced by choosing better storage locations. Better controllers could understand the decay modes and read and rewrite data to maximize expected lifetime, so power is needed for maximal expected lifetime. In practice, all of this is not of much use to everyday people [1]. But if you want to maximize your data retention, study all these issues. Here's a case the authors claim bit rot happened in three months offline [2]. [1] http://www.anandtech.com/show/9248/the-truth-about-ssd-data-retention http://www.anandtech.com/show/9248/the-truth-about-ssd-data-... [2] http://www.maximumpc.com/jedec-your-ssd-needs-power-source-avoid-losing-data-2015/ http://www.maximumpc.com/jedec-your-ssd-needs-power-source-a...
- throwaway7767 11y ago
  > No need to power or refresh, but if you have a cruddy SSD you should keep other backups. No need to power or refresh, but if you have data you value you should keep backups. Seriously, no matter where you are keeping your data, if you don't have a completely independent copy somewhere, you will lose it some day.
pkaye 11y ago
It should be enough because the SSD will schedule a periodic "fsck" equivalent and check for degraded bits to repair.

MCRed 11y ago

It should have no impact. It really is about write capacity. The little cells can only handle being changed so many times before they wear out. The wearing is a chemical/semi-conductor type problem. It's not like DRAM where keeping power applied keeps the cells "fresh" (and in DRAM it's done literally be refreshing each cell at a certain frequency.) The simple equation is the more times a cell is erased the sooner it fails. Write leveling and other software efforts work to spread around or eliminate unnecessary writes. But over the practical life of a drive (5-10 years?) being powered off will not cause them to lose data. Edit: I've been following FLASH technology since before the terms "FLASH" was coined, back when it was called EEPROM -- Electrically Erasable Programmable Read Only Memory, an evolution of PROMs (write once) and ERPOMS (erasable with UV light). If there's a myth out there that flash drives just forget things, I'd like to point out that I've had flash drives (low quality at that) from the 1990s that were left for 20 years and then read successfully! Show some citations of real evidence before you down vote me.

cjensen 11y ago
That's incorrect. Charge leaks very slowly out of cells. It's not a big issue, but it does happen. Powered-on SSD firmware knows about the problem and will maintain the cells. [1] http://www.anandtech.com/show/9248/the-truth-about-ssd-data-retention http://www.anandtech.com/show/9248/the-truth-about-ssd-data-...
- acqq 11y ago
  And AnandTech quotes Intel materials who often boasts to have the most durable drives. Imagine what happens to other ones.
  - philjohn 11y ago
    Samsung back up the 850 Pro with a 10 year/150TB host writes warranty. The trick is moving back 2 processes, which alleviates some of the issues they've faced with the 840 series.
    - acqq 11y ago
      The warranty is certainly not "it will keep the data 10 years without being powered on." We discuss the topic of how long SSDs retain the data when powered off. Intel says, powered off but stored on just 35 degrees C, only 14 weeks, as published by AnandTech: http://images.anandtech.com/doci/9248/3.PNG http://images.anandtech.com/doci/9248/3.PNG And Intel is proud to be more reliable than others. In one of their presentations I've seen they show that they use some very high tech setups (like accelerators!) to measure the degradations fast, and that the other producers fare worse on their tests.
deleted 11y ago
[deleted]
pgeorgi 11y ago
> flash drives (low quality at that) from the 1990s 90s flash is more likely NOR, which doesn't suffer some of the failure modes of NAND. As for NAND, micron would probably not discuss rumors about their technology as fact: https://www.micron.com/~/media/Documents/Products/Presentation/flash_mem_summit_jcooke_inconvenient_truths_nand.pdf https://www.micron.com/~/media/Documents/Products/Presentati... (read disturb on page 19, data retention on page 21)

bifrost 11y ago

No need to power or refresh, but if you have a cruddy SSD you should keep other backups.

ChrisLomont 11y ago
SSDs should suffer the same bit-rot other flash does. JEDEC specs require that a drive that has used 10% of its rewrite capacity it should hold the data for at least 10 years, and this decreases to when a drive has used 100% of its rewrite capacity it should hold the data for at least one year. So to meet specs a consumer drive should fall in between these timeframes. However, cheaper drives may well not completely meet this spec; this is common for many other manufacturing processes. The bit rot also depends on many other factors, the most important being temperature (you cannot outwit statistical mechanics). The next one is a combination of hot neutrons causing bit flips from impurities in the material and from cosmic rays, the latter of which can be reduced by choosing better storage locations. Better controllers could understand the decay modes and read and rewrite data to maximize expected lifetime, so power is needed for maximal expected lifetime. In practice, all of this is not of much use to everyday people [1]. But if you want to maximize your data retention, study all these issues. Here's a case the authors claim bit rot happened in three months offline [2]. [1] http://www.anandtech.com/show/9248/the-truth-about-ssd-data-retention http://www.anandtech.com/show/9248/the-truth-about-ssd-data-... [2] http://www.maximumpc.com/jedec-your-ssd-needs-power-source-avoid-losing-data-2015/ http://www.maximumpc.com/jedec-your-ssd-needs-power-source-a...
throwaway7767 11y ago
> No need to power or refresh, but if you have a cruddy SSD you should keep other backups. No need to power or refresh, but if you have data you value you should keep backups. Seriously, no matter where you are keeping your data, if you don't have a completely independent copy somewhere, you will lose it some day.

pkaye 11y ago

It should be enough because the SSD will schedule a periodic "fsck" equivalent and check for degraded bits to repair.