DiskPerf - xfce4-diskperf-plugin

This plugin displays instant disk/partition performance (bytes transferred per second) for Linux, OpenBSD/NetBSD/FreeBSD and Solaris systems

Usage

Add this plugin to the panel. Right-click on the icon and open the settings. There are three sections:

In the first section, specify which device monitor, the label and the update interval in seconds;
In the second section, specify which activity to monitor; selecting I/O transfer (it is the default) will alow for inserting a max rate;
In the last section, if a combined bar is used for reading and writing or two separate bars; or, if a single bar is preferred, the bar orders and colors can be customised.

Default settings with I/O transfer and a single bar

Busy time monitor with a single bar

Read and write data in two bars