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While I am aware that performing writes on a USB flash drive degrades the life expectancy of the device. I have heard the quantity of writes is anywhere from 100 thousand to 10 million, but I have not heard about number of read operations. Does reading from the device count toward this total?

I am interested in writing only once to a flash drive and setting it to read-only. Then reading files from the device a thousand or more times per day, but am wondering if (at say 1,000 reads per day), the flash drive will need to be replaced within 100 days (assuming a 100,000 r/w cycle lifetime)?

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Yes it does count, afaik. The number does not indicate atomic read writes, but the cycle in which every block has been written to and read once. –  manasij7479 Jun 1 '12 at 4:32
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up vote 4 down vote accepted

There is, for practical purposes, no read limit. There really isn't a write limit either, it's an erase limit. (And, if you've previously written to a block, you need to erase it to write new data to it.)

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So, as long as you only write the one time to the drive, there will not be an issue reading (and only reading) virtually non-stop from the device for a year or more? –  John Jun 1 '12 at 4:43
    
For decades even. –  David Schwartz Jun 1 '12 at 5:14
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It isn't so simple to answer. When you write a file, new blocks are being written. The used blocks are marked as "dirty". So, if you wrote a 10KB file on a 1MB device, it is likely that the 10 KB file will be written all across the blocks in the 1MB device. Only when there are no more "clean" blocks, the flash controller will likely then erase "dirty" blocks.

Your flash drive will last significantly longer than 100,000 writes of the 10K file on a 1MB device.

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Hmm... would this make defragmenting harmful for a flash drive? –  thegrinner Sep 12 '12 at 15:31
    
@thegrinner yes –  Tom Dignan Oct 11 '12 at 15:00
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