iotop - linux
If you need to monitor processes by I/O instead of CPU, you might be used to "iotop" from Linux. iotop does not exist on FreeBSD, but you can use FreeBSD's built-in version of top to do the same thing.

top -m io -o total

lsof -p PID покажет все открытые процессом файлы, сокеты, терминалы...

gstat, iostat, systat -v - freebsd