After bad attempt to update Raspbian version from Jessie to Stretch my Raspberry PI 3 failed to boot (green LED is blinking 4 times).

I tried to reformat microSD card to install new version of Raspbian from Mac but got problems.

I downloaded Raspbian image, balenaEitcher and SD Card Formatter app for Mac OS. After formatting SD card with SD Card Formatter I launched balenaEitcher, selected image and got green checkbox after flashing as well as one small red dot showing that source and destinations checksums do not match.

Tried with 2 different SD card readers with same result.

I decided to format SD card using terminal on mac.

diskutil list

showed list of drives and I tried to format manually with

sudo diskutil eraseDisk FAT32 SDCARD MBRFormat /dev/disk4

got this error

Error: -69830: This operation requires an unmounted disk

This is list of my questions:

1) How can I validate that SD card has no bad blocks? And if there are any - can I use this card, fix it somehow?

2) What about diskutil error? What can I do to format this card?

2 Answers 2


That what @Milliways wrote in his answer. To answer your question about testing for bad blocks on the SD Card: you cannot test it, simply while a SD Card does not have blocks. It has cells with limited live time for writing it. SD Cards today have spare cells that will be used on the fly for defected cells and a logic will always show you a proper SD Card without defects. The SD Card will never report write errors to the operating system. This has also a confusing side effect with cached data for writing. I haven't seen so far a tool that can check for a defect or weak SD Card. You can try to do a read-after-write test with low level path-through raw data writing. What all this means you can look at Detect an SD card that became read-only. But this will additional stress a weak SD Card.


Formatting is unnecessary and a total waste of time - copying an image doesn't care what is on the card.

If you get a checksum error the SD Card is probably worn out (assisted by unnecessary formatting attempts)

  • is there way to check that SD Card is worn out?
    – moonvader
    Jan 7, 2020 at 10:46
  • Aren't checksum errors a sufficient indicator? It IS POSSIBLE you have faulty hardware or software, but just get a new SD Card - they are cheap, and if you have been using it for 3 years it has earned its keep.
    – Milliways
    Jan 7, 2020 at 10:52
  • Can’t do anything with this microSD card, new card is working fine
    – moonvader
    Jan 9, 2020 at 16:42

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