5. I/O Monitoring

We can also monitor CPU usage as well as monitor disk usage with a handy tool known as iostat

pete@icebox:~$ iostat

Linux 3.13.0-39-lowlatency (icebox)     01/28/2016      _i686_  (1 CPU)


avg-cpu:  %user   %nice %system %iowait  %steal   %idle

           0.13    0.03    0.50    0.01    0.00   99.33

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn

sda               0.17         3.49         1.92     385106     212417

The first part is the CPU information:

• %user - Show the percentage of CPU utilization that occurred while executing at the user level (application)


• %nice - Show the percentage of CPU utilization that occurred while executing at the user level with nice priority.user CPU utilization with nice priorities


• %system - Show the percentage of CPU utilization that occurred while executing at the system level (kernel).


• %iowait - Show the percentage of time that the CPU or CPUs were idle during which the system had an outstanding disk I/O request.


• %steal - Show the percentage of time spent in involuntary wait by the virtual CPU or CPUs while the hypervisor was servicing another virtual processor.


• %idle - Show the percentage of time that the CPU or CPUs were idle and the system did not have an outstanding disk I/O request.

The second part is the disk utilization:

• tps - Indicate the number of transfers per second that were issued to the device. A transfer is an I/O request to the device. Multiple logical requests can be combined into a single I/O request to the device. A transfer is of indeterminate size.


• kB_read/s - Indicate the amount of data read from the device expressed in kilobytes per second.


• kB_wrtn/s - Indicate the amount of data written to the device expressed in kilobytes per second.


• kB_read - The total number of kilobytes read.


• kB_wrtn - The total number of kilobytes written.