diskutil no longer gives PID of dissenting process?
Solution 1:
You can use the lsof command in the Terminal to see which processes have which files open. For example for your disk4:
lsof /dev/disk4
or if you have multiple volumes on that disk mounted:
lsof /dev/disk4*
or you can use a mount point like this:
lsof /Volumes/MyDisk
You'll get a list of open files along with the PID of the process that holds the file open. These are the processes that keeps you from unmounting the file systems.