Understanding the 'iostat' Command (with Examples)

The iostat command is a powerful utility used to monitor system input/output device loading by observing the time the devices are active in relation to their average transfer rates. It helps system administrators understand how well their system’s CPU and I/O devices are performing, thereby facilitating system tuning and performance optimization. The tool comes with several options that allow users to customize the information that they receive, making it versatile for numerous performance monitoring tasks.

Use Case 1: Display a Report of CPU and Disk Statistics Since System Startup

Code:

iostat

Motivation:

This use case is beneficial for obtaining a quick overview of the CPU utilization and I/O device statistics since the last system boot. It captures important performance metrics, offering insights into how processes have utilized the system resources over time. This can be particularly valuable for identifying bottlenecks or inefficiencies that could impact system performance.

Explanation:

• The command iostat without any options provides a default report of CPU statistics along with basic information for every disk available on the system.
• The data displayed includes metrics such as CPU utilization (user time, system time, idle time, etc.) and statistics for each disk (number of reads/writes, sectors read/written, etc.)

Example Output:

Linux 5.8.0-55-generic (hostname) 	08/23/2023 	_x86_64_	(4 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          1.25    0.00    0.55    0.02    0.00   98.18

Device             tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               1.03         5.90        12.02   1012302    2081345
sdb               0.43         8.56         5.12   1235214    1259847

Use Case 2: Display a Report of CPU and Disk Statistics with Units Converted to Megabytes

Code:

iostat -m

Motivation:

Using the -m option is advantageous when dealing with large data operations, as it presents data in megabytes per second, which can be more intuitive and easier to interpret than kilobytes, especially when analyzing trends over time. This simplification aids in quick assessments of data throughput, enabling efficient decision-making in real-time scenarios.

Explanation:

• The -m option modifies the default byte units to megabytes in the disk statistics report.
• This allows for quick visualization of data transfer rates at a higher scale, which is often useful for systems handling large datasets or transfers.

Example Output:

Linux 5.8.0-55-generic (hostname) 	08/23/2023 	_x86_64_	(4 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          1.30    0.00    0.60    0.05    0.00   98.05

Device            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
sda              1.05         0.58        1.17       987.43    2053.89
sdb              0.48         1.03        0.48      1234.56    1257.67

Use Case 3: Display CPU Statistics

Code:

iostat -c

Motivation:

Isolating CPU statistics helps in focusing solely on CPU performance without the added complexity of disk statistics. This use-case provides detailed information about the CPU utilization, making it easier to diagnose CPU-level issues such as a high system load or excessive idle time. This can aid in balancing workloads across CPUs or optimizing process performance.

Explanation:

• The -c option specifically filters the output to show only CPU-related statistics.
• It breaks down various parameters like user CPU percentage, system percentage, idle time, etc., offering an insight into CPU load and efficiency.

Example Output:

Linux 5.8.0-55-generic (hostname) 	08/23/2023 	_x86_64_	(4 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          1.75    0.00    0.62    0.03    0.00   97.60

Use Case 4: Display Disk Statistics with Disk Names (Including LVM)

Code:

iostat -N

Motivation:

Understanding which specific disks or Logical Volume Manager (LVM) components are under significant load is critical for storage management and planning. This use-case enables clarity by associating statistics directly with disk names, facilitating precise monitoring of system components or reconfigurations based on performance data.

Explanation:

• The -N option augments disk statistics to include more descriptive names, including those used in LVM setups.
• It aids system administrators in correlating I/O statistics to physical or logical volumes, allowing for focused performance assessments.

Example Output:

Linux 5.8.0-55-generic (hostname) 	08/23/2023 	_x86_64_	(4 CPU)

Device             tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               1.12         6.83       13.44   1101234    2192345
sda1              0.55         3.24        7.90    512342    1203456
dm-0              2.01         6.83       15.55   1340003    2561234

Use Case 5: Display Extended Disk Statistics with Disk Names for Device “sda”

Code:

iostat -xN sda

Motivation:

Providing extended statistics for a specific device, like sda, allows for an in-depth analysis of disk performance. This scrutiny can highlight particular areas for optimization, such as improving read/write speeds or adjusting queue lengths, thereby customizing performance tuning on a per-disk basis.

Explanation:

• The -x option enhances the report with detailed disk usage statistics.
• Combined with -N, it targets detailed insight for specified devices (e.g., “sda”).
• This allows granular monitoring of disk efficiency, latency, and availability.

Example Output:

Linux 5.8.0-55-generic (hostname) 	08/23/2023 	_x86_64_	(4 CPU)

Device            rrqm/s   wrqm/s     r/s     w/s   rkB/s   wkB/s avgrq-sz avgqu-sz   await  r_await w_await  svctm  %util
sda                0.12     1.32    0.45    1.83    8.67   32.80    34.29     0.05    1.29    0.89    1.74   0.77   1.75

Use Case 6: Display Incremental Reports of CPU and Disk Statistics Every 2 Seconds

Code:

iostat 2

Motivation:

Generating incremental reports at fixed intervals is pivotal for observing dynamic system behavior in real-time. Monitoring these statistics live allows administrators to instantly understand the impact of configurations or workloads, facilitating rapid diagnostics and decision-making.

Explanation:

• The integer 2 specifies an interval, in seconds, for how frequently iostat will update and display the statistics.
• This provides an ongoing stream of performance data, reflecting active usage and resource demands as they shift.

Example Output:

Linux 5.8.0-55-generic (hostname) 	08/23/2023 	_x86_64_	(4 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          2.30    0.00    1.05    0.25    0.00   96.40

Device            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               2.20        24.00        20.50     50000       40000

... [next report in 2 seconds]

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          3.10    0.00    1.95    0.35    0.00   94.60

Device            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               1.40        20.00        25.00     60000       50000

Conclusion:

The iostat command is an essential tool for system administrators seeking insights into CPU and disk performance metrics. By leveraging various options, users can obtain both general and detailed statistics, enabling them to diagnose issues, optimize configurations, and manage resources effectively. Whether you need a snapshot of system startup performance or real-time data for dynamic environments, iostat offers the flexibility to cater to a broad range of performance monitoring needs.