iostat - macOS

Overview

iostat is a command-line utility used in macOS to monitor system input/output device loading by observing the time the devices are active relative to their average transfer rates. This utility can help diagnose system bottlenecks that might stem from a high volume of disk I/O operations. It is particularly effective for performance monitoring, statistical reporting, and system debugging by both system administrators and performance analysts.

Syntax

The basic syntax for the iostat command is:

iostat [options] [interval [count]]
  • interval: Specifies the duration (in seconds) between each report. If omitted, iostat will only produce one report.
  • count: Number of reports generated at the specified interval.

Options/Flags

Here are the most commonly used options for iostat:

  • -c [count]: Number of times the report should be generated. Default is once if not specified.
  • -w [interval]: The interval in seconds between each report. The default is once if not specified.
  • -d: Display the device utilization report only (disk activity).
  • -C: Show CPU statistics.
  • -D: Displays disk usage statistics.
  • -g: Display a summary of disk and CPU statistics.
  • -N: Displays the device statistics with the device’s mount point or logical name.
  • -x: Provides extended statistics, a more detailed metrics view.

Examples

  1. Basic Device Stats Every 2 Seconds

    iostat 2

    This command will print the I/O statistics every 2 seconds.

  2. Extended Disk Statistics with Interval

    iostat -d -x 5 3

    This example will display extended disk statistics every 5 seconds, a total of 3 times.

  3. Monitoring CPU and Disk Statistics Together

    iostat -C -D 10

    Show CPU and Disk statistics together with updates every 10 seconds.

Common Issues

  • High system load: Frequent execution of iostat with very short intervals can itself contribute to system load. Reduce the frequency of reports or increase the interval to mitigate this.
  • Misinterpretation of output: Ensure to understand output columns properly to avoid misinterpretations. Outputs like %iowait and tps require clear understanding before conclusions.

Integration

iostat can be integrated with other shell commands or scripts to automate monitoring and logging:

#!/bin/bash
while true
do
  iostat -x 10 1 >> /path/to/log.txt
  sleep 10
done

This script logs extended disk statistics to a file every 10 seconds.

  • vm_stat: Provides information on virtual memory statistics.
  • top: Displays an ongoing view of system resource usage.
  • df: Reports the amount of available disk space being used by file systems.

For further reading and more detailed information, consult the iostat man page or the official Apple developer documentation.