How can System Monitor display disk io?

I can't imagine this is not possible.... but I can't figure out where to enable it.

can't system monitor (gnome-system-monitor) display disk io?

Why you don't use iostat :

sudo apt-get install sysstat

iostat is found in sysstat package .

For example :

iostat -d 30 /dev/sda 

will give you I/O result in 30 s interval

You can try nmon

sudo apt-get install nmon

Try:

nmon

Output Like below:

Press d = Disk Press c = CPU Press r = RAM Press q to exit

You can also give try with:

iostat

Output like below:

Linux 3.16.0-30-generic (client01)    03/01/2016      _i686_  (2 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
      39.73   24.58    2.96    0.26    0.00   32.48

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               3.32        57.31        40.05  119879872   83767716
sdb               1.45        15.02        22.60   31424408   47273012

You can use system monitor from KDE (ksysguard), open it, go to file and click on "download new tabs" then, you can download disc io.

Anyway, lots of tools let you watch disc IO, for example gnome-shell plugins, Unity indicators, KDE plasmoids or conky.