$ sudo iosnoop -d /dev/sda
/usr/bin/iosnoop: line 148: /dev/sda: syntax error: operand expected (error token is "/dev/sda")
Tracing block I/O. Ctrl-C to end.
/usr/bin/iosnoop: line 196: echo: write error: Invalid argument
ERROR: setting -d or -t filter. Exiting.