One of the many treats offered up by this post-truth world we find ourselves in is the rise (and rise, and rise, and…) of scams, counterfeits, and fraud in just about every sphere. But rather than waffling on too much about the ills of large society, I’ll just record here a sound way to check if that SD card you bought online actually has the capacity it claims.

We’ll be using f3probe, a command provided by the ‘f3’ package available in the Arch User Repository (AUR).

The below command does a full write and read back across the drive and reports back on whether it is true to it’s word or counterfeit.

WARNING: Any data on the drive will be erased!

f3probe --destructive --time-ops /dev/mmcblk0

Replace /dev/mmcblk0 with a full path to the flash/thumb/SD drive in question and wait for it to complete.

Be aware that on large and/or slow drives this could take some time. For a good quality SD card in 64GB it should take only a few minutes but may take as much as 15.