OS X tool (easily portable to other *nixes) that writes random data to a disk (e.x. SD card) and reads it back, comparing hashes of the data. Use with caution.

full-disk-check

#!/usr/bin/env bash

set -eu

disk_file="$1"

bytes="$(diskutil info "$disk_file" | grep -Eo '\(\d+ Bytes\)' | grep -Eo '\d+')"
block_size="$((1024 * 1024))"
blocks="$((bytes / block_size))"

read -p "Are you sure you want to unmount and overwrite $disk_file? " -n 1 -r; echo
if [[ $REPLY =~ ^[Yy]$ ]]; then
  diskutil unmountDisk "$disk_file"

  dd bs="1m" count="$blocks" if="/dev/urandom" 2>/dev/null | tee >(md5 1>original.md5) | dd of="$disk_file"
  dd bs="1m" count="$blocks" if="$disk_file" | md5 >result.md5

  cat original.md5 result.md5
  rm original.md5 result.md5
fi