check that sdcard that how much actually it could contain data

verify-sdcard.sh

#!/bin/sh

SDCARD="$1"

RANDFILE="/tmp/rand10m"
TMPBIN="/tmp/tmp.bin"
MAGICWORD="--i-know-what-i-am-doing"
BS="10240"
COUNT="1024"

[ -z "$2" ] && \
{ echo "Usage: $0 /dev/sde ${MAGICWORD}"; exit; }

[ "$2" != "${MAGICWORD}" ] && \
{ echo "Well, please use magicword"; exit; }

[ -f "${TMPBIN}" ] && sudo rm -f ${TMPBIN}

if [ ! -f "${RANDFILE}" ]; then
	dd if=/dev/random of=${RANDFILE} bs=${BS} count=${COUNT}
fi

RANDSUM=$(md5sum ${RANDFILE} | cut -f1 -d' ')
FILESZ=$(expr ${BS} \* ${COUNT})

C=0
while true; do
	ISEEK=$(expr ${C} \* ${COUNT})
	OSEEK=${ISEEK}

	C=$(expr ${C} + 1)

	echo "===== [$C] ====="
	echo "=== Write [$C] ==="
	sleep 1
	sudo dd if=${RANDFILE} of=${SDCARD} bs=${BS} \
		count=${COUNT} oseek=${OSEEK} status=progress conv=sync
	echo ""

	echo "=== Read [$C] ==="
	sleep 1
	sudo dd if=${SDCARD} of=${TMPBIN} bs=${BS} \
		count=${COUNT} iseek=${ISEEK} status=progress conv=sync
	echo ""

	echo "=== MD5CHECK [$C] ==="
	sleep 1
	SUM=$(md5sum ${TMPBIN} | cut -f1 -d' ')
	if [ "${SUM}" != "${RANDSUM}" ]; then
		echo	"FAILED : SUM = ${SUM}"
		break
	else
		echo "OK"
	fi
	echo ""
done