Just learnt that DTrace can’t be run at full pelt when rootless Mac OS X feature is enabled. For example, iotop ends like this:
: probe description io:::start does not match any probes
And it seems that the only way out is to boot into a rescue mode and run csrutil disable to turn off the protection mode. Only after that you could call your best friends like iotop, iosnoop and many others which are published at DTrace Book page.
Btw, if you haven’t bought it yet I highly recommend to do so.