Monitoring Transfer Rates and Transfers per Second using iostat

iostat is useful to monitor both transfer rates and transfers per second, commonly called IO's per second (IOPS).  For example:

# Monitor all block devices
$ iostat -dk 1

# Monitor a single block device
$ iostat -dk 1 fioa
Linux 2.6.27.24-170.2.68.fc10.x86_64 (fusion-io-live)
Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
fioa           2557.91         1.61     86473.04        517   27712880

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
fioa           5223.00         0.00    668544.00          0     668544

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
fioa           5219.00         0.00    668032.00          0     668032

(NOTE: The first line of output from iostat should be disregarded, because it represents a cumulative amount before the iostat command began running.)

The two interesting columns above are transfers per second (tps) and kilobytes written per second (kB_wrtn/s).  The transfers per second (tps) are equivalent to IOPS.

In this example, 668,000 KB per second (kB_wrtn/s) are being written to the iodrive at a rate of 5219 transfers per second or IOPS.

Older versions of iostat are limited to showing the transfers in kilobytes per second (KB/s).

Newer versions of iostat include the “-m” switch in order to see megabytes per second (MB/s).

$ iostat -dm 1 fioa

The iostat utility is included in a larger software package called sysstat.  It is easily installed by issuing “yum install sysstat” (Red Hat/CentOS/Fedora) or by running “apt-get install sysstat” (Debian/Ubuntu).