zfs-test/bin/create-test-setup/edit-part-of-file

#!/bin/sh
dd if=/dev/urandom of=random-1M bs=1M count=1
zfs snap tank/test@first
sleep 0.001 # sleep long enough to ensure mtime is different
dd if=/dev/urandom of=random-1M bs=1k count=1 conv=notrunc