I have a micro SD card from Kingston - 32GB class 10

When i'm writing on it using usb card reader or my phone, average write speed is about 6MB/s

But after about 10GB of data written into it, transfer dramatically drops to 200Kb/s

I have tried formatting it with different allocation unit sizes, it doesn't make any difference

any ideas ?



additionally, when i use it filled above 10GB of data in my phone (taking pictures, listen music, using applications that write on it) files sometimes go missing


The limit seems to be not 10GB but about 8 300 000 000 bytes

  • Test more things. Does it return to normal speeds after cooling? Even real hot I have never seen a speed drop, but some adaption methods keep the heat in more, double insulated. Does it return to normal speeds after removing the USB (not the card) and replacing the USB. (the usb dropping back to compatability mode)? Checking for the USB mode the reader is operating in via the OS (I forget how you do that). There are a lot of bad readers out there now also, even from the high branded names they are making them as cheep as possible, try a different reader. – Psycogeek Sep 27 '14 at 21:47
  • I doesn not back to normal after cooling. Replugging the USB also doesnt help. I uset two different readers (one microsd reader, second SD reader with card in microsd adapter) both are cheap, but same thing happends in my phone (lenovo ...) – user372977 Sep 28 '14 at 9:58
  • yea, same thing with the phone, that indicates it has more to do with how your computer USB is handling things, or the flash. Indicating that data fails to show up, you probably have a bad or clone chip. For the flash chip I would want to FILL it up completly even taking days to do so, then test if that data is 100% there by comparing it fully. could be the data is going nowhere? – Psycogeek Sep 29 '14 at 23:10
  • when i said about phone, i didnt mean phone connected by usb to PC. I meant phone alone, copying files from internal phone memory to SD card – user372977 Sep 30 '14 at 16:09
  • The card may have been damaged by improper formatting. You can try reformatting it properly but it may be hopeless. – David Schwartz Sep 30 '14 at 16:18

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