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It has been said that continuous writing on an SD card can cause wear and tear on the memory cells, which can eventually lead to the failure of the card. One of the answer to my question here How to achieve SD card's life service to 10 years or more? said that flash memories have limited amount of write cycles (10k to 100k average). If given a scenario were an SD card has 64GB capacity and it consumed only 5GB of written data, do you think it will soon experience wear and tear or perhaps failure if this 5GB used space reached the 100K write cycle eventhough there is still ample amount of unused space?

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    100k means SLC card (single layer cell). As a normal consumer you don't get SLC cards anymore (because they store less for the same price). So the title should be amended. SLC cards can still be found as "industrial grade" on some specialized sites. here's a site showing their expected write life: kingston.com/en/blog/pc-performance/…
    – A.B
    Feb 11 at 11:29
  • Thanks @A.B for sharing the information, so write cycles depends as well on the type of NAND flash storage used in the card. Feb 11 at 14:11
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    The max write cycle count is the max write cycle count (yes that depends on SLC, MLC TLC, QLC etc.). FTL is a way to avoid to reach this write cycle count. Don't confuse them. What you need is to know the final effect. But that's left to answers.
    – A.B
    Feb 11 at 14:13
  • If this is with regard to memory cards in cameras, you might want to consider getting a camera which can write to two cards for each photo. Feb 11 at 19:32
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    @Mast SD cards and USB sticks are both equally unreliable, because most products on market are cheaply made trash that barely conforms to standards. Source: My personal experience with trying to solve removable media problems in embedded devices for over 10 years.
    – user694733
    Feb 12 at 9:52

1 Answer 1

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Good information is to be found in the post Quick reminder that SD cards with wear-leveling are now fairly common (i.e. WD Purple microSD) from 2019:

Vast majority of SD cards do not have wear-leveling, and might keep on writing to the same blocks over and over. In the end you wear out the card, and it becomes defective.

SD cards with wear-leveling used to be expensive, and small in size, and were usually reserved for specialized use (i.e. industrial applications). Today, you can get a 64GB SD card with WL for as low as 15 EUR.

Keep in mind that even though the manufacturer of the SD card might use terms such as "high endurance" on their product, you have no guarantee the card actually employs wear-leveling. Unless it's specifically stated in the specs, it's safe to assume a "high endurance" card will not have wear-leveling.

The author got this statement from WD Engineering regarding his wear leveling inquiry:

Our WD Purple MicroSD's do both static and dynamic wear-leveling. Meaning all blocks across whole address space are considered for wear leveling regardless of if and how the blocks are used. This keeps the number of program erase cycles consistent on all blocks.

The answer is then that if a portion of the card is used again and again, its failure means the failure of the card. You should look for cards that support wear-leveling, in order to distribute the load over the entire card (although finding this spec might not be easy).

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  • Oh I see, thanks @harrymc, so the key factor is the wear-leveling technique, a must have to SD card choice when longer life span is of utmost concern. I found this Kingston Industrial microSD which has the wear-leveling feature kingston.com/datasheets/sdcit2_us.pdf, I'll try this out as WD Purple microSD is not available online in our area. Feb 11 at 14:07
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    Are there no OSes or drivers that would do the wear-leveling in software?
    – trlkly
    Feb 12 at 5:30
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    @trlkly There are filesystems that do so -- notably including JFFS and its successors -- but these require special support from the OS and are not as easily transferable to other systems like the more ubiquitous filesystems. (This is usually why cards will be preformatted with some kind of FAT, as the de facto standard filesystem, though you can of course reformat them however you like.) The hardware implementation means a general filesystem can be used instead (and indeed the special one may now be worse).
    – Miral
    Feb 12 at 6:30

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