iostat reports the accumulated device usage rather than collecting it on a process- or thread-basis. Reads and writes are broken down by block-device. Together with other tools, such as sar, iostat is part of the sysstat collection.

iostat is used by specifying an interval measurements are taken at as a positional argument iostat 2 will display a new measurement every 2 seconds.

Extended statistics can be requested using the -x option. Each of the data-fields is documented in the iostat man page.

For each interval two data blocks are shown, the first one shows the CPU usage (averaged over all CPUs) while the second shows the usage of each block device.

Linux 4.4.3-1-ARCH (your-hostname) 	03/10/2016 	_x86_64_	(8 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          13.25    0.24    2.37    0.04    0.00   84.10

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda              12.08        81.48      1538.83     947077   17886516
sdc               0.03         0.58         0.01       6777         80
sdb               0.01         0.47         0.00       5432          0

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           7.46    0.00   12.85    0.00    0.00   79.69

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               0.00         0.00         0.00          0          0
sdc               0.00         0.00         0.00          0          0
sdb               0.00         0.00         0.00          0          0

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           7.63    0.00   12.77    0.00    0.00   79.60

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               1.00         0.00        24.00          0         48
sdc               0.00         0.00         0.00          0          0
sdb               0.00         0.00         0.00          0          0