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It's almost common knowledge that excessive writes (including formatting, defragmenting etc) will, in time, wear out solid state drives. But does reading lots of data from SSD's cause wear too?

I'm planning on enabling prefetching on a Linux machine with a SSD. I have atime disabled.

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    I would note that, while it's common knowledge, most people vastly overestimate how fast they'll run out of writes on an SSD. Intel specifically states you can write over 21GB a day for ten years straight without exhausting the writes on their consumer-level drives.
    – Shinrai
    Jun 22, 2012 at 14:08
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    (Also, never defragment an SSD anyway, since it won't actually do anything useful.)
    – Shinrai
    Jun 22, 2012 at 14:08
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    Think of bending a piece of metal (like a coat-hanger). You can “write” information into it (e.g., straight=0, bent=1) by bending it, and “read” information by looking at it. You can read it as many times as you want without (significant) harm, but you can only write to it so many times before it breaks.
    – Synetech
    Aug 19, 2013 at 4:44
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    @Synetech - My impression is that the physical location of data on an SSD is both A: largely irrelevant in 99% of circumstances and B: Not properly understood by most defragmentation software since they're written expecting hard drives, and also the controller on the drive handles most of that stuff (things getting put in different places for wear leveling purposes, etc). Vastly oversimplifying here of course.
    – Shinrai
    Aug 19, 2013 at 4:46
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    Almost all of the information in these comments is out of date.
    – David Schwartz
    Dec 11, 2015 at 16:31

4 Answers 4

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Doesn't affect the device. The limited write lifetime of Flash is a natural consequence of how they work.

Data on Flash drives is safe because the bits are stored by electrons locked in a very well isolated layer. These electrons, if present, produce an electric field that can be picked up by a nearby transistor. Since they're locked up, reading out the transistor doesn't affect the electrons. During writes, however, to get the electrons through that layer Flash needs very high voltages. These high voltages cause some damage to the isolation layer, which accrues.

In comparison, DRAM doesn't have such an isolation layer. The electrons move quite easily. As a result, DRAM is faster and doesn't break down from writes, but the leaked electrons frequently need to be replaced. Turn off the power and they're all gone in milliseconds.

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    Although reads themselves are not directly harmful, it is worth noting that excessive reads can cause the firmware to generate background writes. That said, the background writes will probably be insignificant in most cases. More info: superuser.com/a/725145/6091
    – rob
    May 8, 2014 at 17:10
  • beautiful answer
    – cedbeu
    Mar 20, 2020 at 2:52
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I don't believe the read process affects the NAND cells although I could be wrong (for example, look towards the bottom of this article). It may be that if a "page" or eraseblock is not reprogrammed in a very long time there is a (probably very small) likelihood some of the bits will revert to an unprogrammed state. Not sure if firmware takes this into account and rewrites/remaps pages that haven't been read in a long time.

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  • Interesting. Do you happen to have more information (than just that article) about this behavior?
    – dtmland
    Feb 28, 2014 at 16:07
  • I don't unfortunately but will try to remember to update if I encounter further info.
    – LawrenceC
    Mar 1, 2014 at 18:54
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    It's worth noting that the reads themselves are not harmful, but excessive reads can cause the firmware to generate background writes to counteract retention errors and read errors. @dtmland See my answer to a similar question that was inspired by ultrasawblade's answer. superuser.com/a/725145/6091
    – rob
    May 8, 2014 at 16:59
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The reliability section of this table does not mention it, so I assume reads do not affect the drive.

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    That would be my assumption as well, but I would like to be very sure – disabling prefetching is free, new SSDs cost a fortune.
    – Wander Nauta
    Jun 22, 2012 at 13:18
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Flash memory is just an eeprom (a chip that can be reprogrammed. It is the reprogramming that causes wear, reads are unlimited. For reading its just memory. http://en.wikipedia.org/wiki/Flash_memory#NAND_flash this article talks a bit about how the reprogramming works, and how it basically 'burns' the data into memory.

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    Flash !== EEPROM
    – Alvin Wong
    Jun 22, 2012 at 13:28
  • Yeah, it's not technically EEPROM, but this is still true in that reads don't cause any damage.
    – Shinrai
    Jun 22, 2012 at 14:07

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