Parallel dd to test multiple file writes and multiple device reads using simple `dd` methods

paradd.sh

#!/bin/bash                                                                                                                             
declare MBYTES=2048                                                                                                                     
declare -a BLK_DEVS FILES                                                                                                               
#set -x                                                                                                                                 
                                                                                                                                        
_usage() {                                                                                                                              
        cat <<EOF                                                                                                                       
Usage:                                                                                                                                  
  $0 <-r|-w> [options ...]                                                                                                              
                                                                                                                                        
Wrapper for standard read/write block device tests using dd in parallel                                                                 

Options:
  -d    Read device name (i.e. /dev/sda) : Can be used more than once
  -f    Write file name and path (i.e. /tmp/testfile) : Can be used more than once
  -b    Size in MiB, Default: 2048
  -w    Write operation test
  -r    Read operation test

Examples:
  Test reading 1GiB of data from devices /dev/sda and /dev/sdb:

    $0 -r -d /dev/sda -d /dev/sdb -b 1024
    $0 -r -d sda -d sdb

  Test writing 2GiB of data to files ~/testfile and /tmp/testfile:

    $0 -w -f ~/testfile -f /tmp/testfile
EOF
}

_drop_caches() {
        echo 3 > /proc/sys/vm/drop_caches
}

_dd_test_read() {
    _drop_caches
        local device="${1:?ERROR missing device name(s)}"
        local mbytes="${2:?ERROR Missing output filesize}"
    dd if="/dev/$1" of=/dev/null bs=1M count="$2" 2>&1 | grep copied
}

_dd_test_write() {
        _drop_caches
        local file="${1:?ERROR Missing filename(s)}"
        local mbytes="${2:?ERROR Missing output filesize}"
        dd if="/dev/zero" of="${file}" bs=1M count="${mbytes}" conv=fdatasync 2>&1 | grep copied
        rm -v "${file}"
}

while getopts ":d:b:rwhHf:" opt; do
        case $opt in
                d) BLK_DEVS+=( "${OPTARG//\/dev\//}" ) ;;
                f) FILES+=( "${OPTARG##\/dev*}" ) ;;
                b) MBYTES="$OPTARG"  ;;
                w) OPERATION="write" ;;
                r) OPERATION="read"  ;;
                [Hh]|*) _usage; exit 1 ;;
        esac
done
typeset -p FILES BLK_DEVS


if [[ "$OPERATION" == "read" ]]; then
        for (( i=0; i<${#BLK_DEVS[@]}; i++ )); do
                ( _dd_test_read "${BLK_DEVS[i]}" "${MBYTES}" )&
        done
elif [[ "$OPERATION" == "write" ]]; then
        for (( i=0; i<${#FILES[@]}; i++ )); do
                ( _dd_test_write "${FILES[i]}" "${MBYTES}" )&
        done
else
        echo "Please specify either -r for read or -w for write testing"
        _usage
fi
wait