iostat

This command will produce output that shows the average CPU load and disk I/O statistics since the last system boot. The first section gives CPU usage percentages (user, system, idle, etc.), and the subsequent sections list I/O data for each device, including metrics such as  tps (transactions per second),  kB_read/s, and  kB_wrtn/s.

Real-Time Monitoring

To monitor disk I/O in real-time, you can use the  -x flag for extended statistics and specify an interval. For example, to display updated statistics every 2 seconds:

iostat -x 2

This command will continuously refresh the output every 2 seconds, giving you a live view of CPU and I/O activity.

Monitoring Specific Devices

If you want to monitor a specific device, you can specify it by name. For example, to monitor only  /dev/sda, run:

iostat -x 2 /dev/sda

This will show statistics for the specified device only, which is useful if you are troubleshooting or monitoring a particular disk.

Display Historical Data

The  iostat tool can also display historical data collected by the  sysstat service. To view I/O activity from a previous day, use the  -h flag along with the  -p flag for partitions. For example:

iostat -h -p ALL

This will give you a detailed historical view of all devices and partitions.

Helpful Tips

1. Understanding Key Metrics:

   • %util: This is the percentage of time the device was busy. If it's consistently close to 100%, the device may be a bottleneck.
   • await: This indicates the average time (in milliseconds) for I/O requests to complete. High values here might indicate an I/O bottleneck.
   • tps: Transactions per second, a measure of the number of I/O operations per second. A high number of transactions might be normal for a busy disk, but if combined with high  await and  %util, it can indicate problems.

2. Regular Monitoring: Set up cron jobs to run  iostat at regular intervals and log the output to a file for later analysis. For example, adding this line to your crontab will log disk I/O every 10 minutes:

   */10 * * * * /usr/bin/iostat -x >> /var/log/iostat.log

3. Combine with Other Tools:  iostat is great for I/O-specific monitoring, but combining it with other tools like  top or  htop for CPU and memory monitoring, and  iotop for per-process I/O, can give you a more holistic view of system performance.

https://www.howtoforge.com/how-to-install-and-use-iostat-on-debian-12/?__cf_chl_tk=TmGeD6lGBQ8oDTcuZId5Ih83DwVRDOxtH6Jvm2b0lrQ-1725066004-0.0.1.1-4991