low-level IO using `dd` in parallel.

dd_parallel.sh

#!/usr/bin/env /bin/bash

##
# dd_parallel.sh
# Low-level IO to disks using 'dd' in parallel.
# ref: https://unix.stackexchange.com/a/160526/217521
##

usage() {
  echo "Usage: $0 -i <input_file> -o <output_file> -b <block_size:512000B> -c <count:1000> -s <status:progress>"
  exit 1
}

while getopts ":i:o:b:c:s:" opt; do
  case $opt in
      i) INFILE="$OPTARG"
         ;;
      o) OUTFILE="$OPTARG"
         ;;
      b) BLOCKSIZE="$OPTARG"
         ;;
      c) COUNT="$OPTARG"
         ;;
      s) STATUS="$OPTARG"
	 ;;
      *) usage
         ;;
  esac
done

##
# handle required args
##
if [ -z "$INFILE" ] || [ -z "$OUTFILE" ]; then
    usage
fi

##
# Compute the output device size
##
OUTSIZE=`python -c $'import os; p = os.popen("sudo fdisk -l '"${OUTFILE}"'"); print(p.readlines()[0].split(",")[1].strip().split(" ")[0].strip())'`

##
# handle optional args
##
if [ -z "$STATUS" ]; then
    STATUS="progress"
fi

if [ -z "$BLOCKSIZE" ]; then
    BLOCKSIZE="512000"
fi

if [ -z "$COUNT" ]; then
    COUNT="1000"
fi

##
# Execute
##
NSEQ=$(($OUTSIZE / $BLOCKSIZE))
seq 0 $COUNT $NSEQ |
    parallel -k \
	     sudo dd \
	     if=$INFILE \
	     bs=$BLOCKSIZE \
	     skip={} \
	     conv=sparse \
	     seek={} \
	     count=$COUNT \
	     of=$OUTFILE \
	     status=$STATUS