quick and dirty sdcard (microsd) flash test script (and links). Comments are welcome.

f3 usage

F3(1)                        test real flash memory capacity                       F3(1)

NAME
       f3write, f3read - test real flash memory capacity

SYNOPSIS
       f3write [--start-at=NUM] [--end-at=NUM] <PATH>
       f3read  [--start-at=NUM] [--end-at=NUM] <PATH>

DESCRIPTION
       F3  (Fight  Flash  Fraud  or Fight Fake Flash) tests the full capacity of a flash
       card (flash drive, flash disk, pendrive). It writes to the card and  then  checks
       if can read it. It will assure you haven't been sold a card with a smaller capac‐
       ity than stated.

       When writing to flash drive, f3write fills the filesystem with  1GB  files  named
       N.h2w, where N is a number (i.e. /[0-9]+/).

       WARNING: all data on the tested disk might be lost!

OPTIONS
       --start-at=NUM
              Initial number of file names. Default value is 1.

       --end-at=NUM
              Final number of file names. Default value is "infinity".

EXAMPLE
       To write over a flash drive mounted at /media/TEST:

             $ f3write /media/TEST

       To read this flash drive:

             $ f3read /media/TEST

SEE ALSO
       For detailed information about the F3 tools, see:

       http://oss.digirati.com.br/f3/

AUTHOR
       F3  was written by Michel Machado <michel@digirati.com.br>.  This manual page was
       first written by Joao Eriberto Mota Filho <eriberto@eriberto.pro.br>.

sdcard-test.bash

#!/bin/bash

# SDCARD test script
# autor Marc Quinton / august 2017

# usefull links : 
# - f3 : http://oss.digirati.com.br/f3 (sdcard test program) ; https://linuxreviews.org/HOWTO_test_SD_cards_and_identify_fake_ones_(mostly_sold_on_ebay)
# - scanflash : https://github.com/Malvineous/scanflash

dd if=/dev/urandom bs=1M count=512 of=data

# mount your SDCARD and go to directory
# create 1 random data file

# then duplicate this file until no space left on SDCARD.
# when disk is full, for loop will exit.
for i in $(seq 130) ; do 
  f=$(printf "%02d" $i)
  echo $f
  cp data $f || break
  sync
done

# flush buffer and empty system buffers
sync ; sync; sync
echo 3 > /proc/sys/vm/drop_caches

# compute MD5SUM for each files
md5sum data ??

# how much data as been writen on disk :
du -sm .

# is there any free disk space;
# many times, "fake sdcards claims to have more space than real 
df -H

install f3 (Fight Flash Fraud) on debian (ubuntu) : apt install f3

• usage : man f3write.