@kaia >Linux
`dd --version`

Here, have a GNU bash function that tells you how much data Linux has claimed to have written, but hasn't in fact done so yet;
watchSync() {
watch -n1 'grep -E "(Dirty|Write)" /proc/meminfo; echo; ls /sys/block/ | while read device; do awk "{ print \"$device: \" \$9 }" "/sys/block/$device/stat"; done'
}