Sunday 23 December 2018

Unable to read an SD card on Linux: SanDisk ExtremePro 64GB 95MB/s

For at least the last 10 years I've considered Linux to be the gold-standard operating system when checking memory devices.


If a drive could not be read on Windows, I'd test it on Linux to see if it had really failed.

But Linux didn't respond to an SD card recently, although the card was clearly working OK.

A few weeks ago we bought a new mirror-less camera which came with two almost identical SD cards. Same make, same model, same capacity ...the only difference was the speed. The format on both cards was exFat, a format that I was not familiar with.

low fat

Microsoft introduced exFat (extended FAT) in 2006 as a file system optimised to support useful memory devices, such as memory sticks & SD cards, for the embedded operating system Windows CE. Unfortunately, unlike regular FAT/FAT16/FAT32, exFAT is protected by Microsoft patents (Booo...) although it can still be read on Linux, thanks to some Russian guy on Github ...(...Hooray!).

So for Debian based distros, type:-

sudo apt install exfat-fuse exfat-utils install the necessary.

I just can't see it

However, it wasn't the lack of exFat support on my Lubuntu laptop that stopped the system recognising this particular SD card. Using the disk/file system command:-

df -hT

...worked on the faster, 300MB/s SD card, giving an output that included the line:-

/dev/mmcblk0p1 fuseblk    60G  5.3G   55G   9% /media/steve/LUMIX_300MBs

But this didn't work for the 95MB/s SD card.

And checking the logs I find this System error:-

mmc0: error -110 whilst initialising SD card

I spent a lot of time searching the net, and found a lot of useless forum comments. Some people suggest that this error means your card is dead, despite being advised by the OP that the card works on other systems.

Some suggest that it is a low level problem in the kernel, and some have had success by adding a new file:-


The suggested contents of this file is something like:-

 mmc0:options sdhci debug_quirks2=0x2

...but everyone has their own magic incantations.

My workaround was to dig out an 'old school' card reader (its good that I never chuck anything away!).

95MB/s problem card with reader & the readable 300MB/s card

With the troublesome SD card mounted in the card reader, I can access the files OK.

However, we are unlikely to use this card except maybe in an emergency, as we will have to dig out the old card reader just to scrape the photos off of it!

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