Disk Monitoring — Monitoring Storage Usage and Disk Health¶

Disk Monitoring is the process of tracking disk space, filesystem usage, inode consumption, disk I/O performance, and storage health to ensure Linux systems continue operating reliably. Running out of disk space or experiencing storage performance issues can cause application failures, database corruption, logging problems, and even system crashes. Every Linux administrator, DevOps engineer, Cloud Architect, Platform Engineer, and Site Reliability Engineer (SRE) should know how to monitor storage resources proactively in production environments.

Learning Path¶

Linux Mastery → Module 12: Monitoring & Logs → Lesson 5

Difficulty: Beginner → Intermediate

Reading Time: 95 Minutes

Course Progress

Course: Linux Mastery

Module: Monitoring & Logs

Lesson: 5 of 10

What You'll Learn¶

After completing this lesson, you'll be able to:

Monitor disk space usage
Analyze filesystem utilization
Monitor inode usage
Identify large files and directories
Understand disk I/O
Monitor storage performance
Troubleshoot disk space issues
Apply production monitoring best practices

Prerequisites¶

Complete:

Modules 1–11
Module 12 Lessons 1–4

Why Learn Disk Monitoring?¶

Imagine a production database server.

Without monitoring:

Disk Becomes Full

↓

Database Stops Writing

↓

Application Failure

↓

Downtime

With proactive monitoring:

Disk Usage

↓

Alert at 80%

↓

Cleanup or Expand Storage

↓

No Downtime

Monitoring storage prevents many production outages.

What is Disk Monitoring?¶

Disk monitoring involves tracking:

Disk capacity
Filesystem usage
Inode usage
Disk I/O
Storage performance
Disk health
Storage growth

Disk Monitoring Architecture¶

Disk

↓

Filesystem

↓

Linux Monitoring Tools

↓

Administrator

↓

Corrective Action

Check Disk Space¶

The most common command:

df -h

Example:

Filesystem      Size Used Avail Use%

/dev/sda2       100G 60G 40G 60%

Options:

-h → Human-readable
-T → Display filesystem type

Check Filesystem Types¶

df -Th

Example:

ext4

xfs

Monitor Inode Usage¶

Sometimes disk space is available, but no new files can be created because all inodes are used.

Check inode usage:

df -i

Example:

IUsed

IFree

IUse%

Find Large Directories¶

Use:

du -sh /*

Check a specific directory.

du -sh /var/*

Example:

15G /var/log

Find Large Files¶

Example:

find / -type f -size +500M

Find files larger than 500 MB.

Sort Directory Sizes¶

du -ah /var | sort -rh | head -20

Shows the largest files and directories first.

Check Mounted Filesystems¶

mount

Or:

findmnt

Useful for verifying storage mounts.

Disk Usage by Filesystem¶

lsblk

Example:

Disk

↓

Partition

↓

Mount Point

Display filesystem information.

lsblk -f

Monitor Disk I/O¶

Install sysstat if needed.

iostat

Extended statistics.

iostat -x

Shows:

Read operations
Write operations
Utilization
Wait times

Monitor Real-Time I/O¶

iotop

Displays processes performing disk I/O.

Requires root privileges on many systems.

Check Open Files¶

Sometimes a deleted file still consumes disk space because a process keeps it open.

View open files.

lsof

Deleted files:

lsof | grep deleted

Check Disk Usage of a Directory¶

du -sh /home

Human-readable summary.

Check Available Space¶

df -h /

Monitor the root filesystem regularly.

Filesystem Health¶

For ext4 filesystems:

sudo fsck /dev/sda1

Warning

Run fsck only on unmounted filesystems or in maintenance mode unless the filesystem specifically supports online checking.

For XFS:

xfs_repair

Run only on an unmounted filesystem unless instructed otherwise.

SMART Disk Health¶

Install SMART tools.

smartctl -H /dev/sda

Displays disk health.

Detailed information.

smartctl -a /dev/sda

Requires:

smartmontools

Common Commands¶

Check disk space.

df -h

Directory usage.

du -sh

Monitor inodes.

df -i

Largest files.

find / -size +500M

Disk I/O.

iostat -x

Real Production Examples¶

Check root filesystem.

df -h /

Find large log files.

find /var/log -type f -size +100M

Monitor I/O.

iostat -x

View deleted open files.

lsof | grep deleted

Production Perspective¶

Disk monitoring is essential for:

Database servers
Kubernetes nodes
Web servers
Logging servers
CI/CD systems
Virtual machines
Cloud infrastructure
Enterprise storage systems

Storage issues are among the most common causes of production outages.

Hands-on Lab¶

Task 1¶

Check filesystem usage.

df -h

Task 2¶

Check inode usage.

df -i

Task 3¶

Display the largest directories under /var.

du -sh /var/*

Task 4¶

Find files larger than 500 MB.

find / -type f -size +500M

Task 5¶

Display mounted filesystems.

findmnt

Task 6¶

Display block devices.

lsblk -f

Task 7¶

Monitor disk I/O.

iostat -x

Task 8¶

Check disk SMART health (if supported).

smartctl -H /dev/sda

Command Deep Dive¶

Command	Purpose	Production Example
`df -h`	Display filesystem usage	Capacity planning
`du -sh`	Directory usage	Storage analysis
`df -i`	Monitor inode usage	Filesystem troubleshooting
`find`	Locate large files	Disk cleanup
`iostat -x`	Monitor disk I/O	Performance analysis
`smartctl`	Check disk health	Hardware monitoring

Common Disk Monitoring Mistakes¶

Mistake	Solution
Monitoring only disk space	Monitor inode usage and I/O as well
Ignoring log growth	Configure log rotation
Never checking disk health	Monitor SMART status
Waiting until disks are full	Configure alerts before capacity limits
Deleting files without checking open file handles	Use `lsof` to verify deleted files are not still in use

Production Troubleshooting Scenario¶

Scenario

A production application reports:

No Space Left on Device

Investigation:

df -h

Disk usage:

100%

du -sh /var/*

Findings:

/var/log

↓

Large Log Files

The administrator archives old logs, verifies logrotate is functioning correctly, and restores normal disk usage.

Best Practices¶

Monitor disk space continuously.
Configure alerts before disks become full (for example, at 80% usage).
Monitor inode usage in addition to disk capacity.
Rotate and archive logs regularly.
Review disk I/O performance.
Monitor SMART health for physical disks.
Plan storage expansion before capacity limits are reached.
Include storage monitoring in centralized monitoring platforms such as Prometheus and Grafana.

Common Mistakes¶

❌ Monitoring only available disk space.

✅ Avoid this mistake: monitoring only available disk space.

❌ Ignoring inode exhaustion.

✅ Always review inode exhaustion.

❌ Never reviewing disk I/O performance.

✅ Always reviewing disk I/O performance.

❌ Allowing log files to consume all available storage.

✅ Do not allow log files to consume all available storage.

❌ Ignoring SMART warnings from storage devices.

✅ Always review SMART warnings from storage devices.

Interview Questions¶

Beginner¶

What does df -h display?
What is the difference between df and du?
Why are inodes important?
Which command lists mounted filesystems?

Intermediate¶

How do you identify large files consuming disk space?
What information does iostat -x provide?
Why can "No space left on device" occur even when free disk space exists?
How do you check whether deleted files are still open?

Architect Level¶

How would you monitor storage across hundreds of Linux servers?
How would you design alert thresholds for production storage monitoring?
How would you troubleshoot a Kubernetes node experiencing high disk I/O?

Summary¶

In this lesson, you learned:

Disk space monitoring
Filesystem usage
Inode monitoring
Large file identification
Disk I/O analysis
Filesystem health
SMART monitoring
Production storage monitoring best practices

Disk monitoring is essential for maintaining healthy Linux systems. By continuously monitoring storage capacity, inode utilization, disk performance, and hardware health, administrators can prevent outages, improve performance, and ensure reliable operation of production workloads.

Key Takeaways¶

Use df -h to monitor filesystem capacity.
Use du to identify large directories and files.
Monitor inode usage with df -i.
Analyze disk performance using iostat.
Monitor physical disk health using SMART tools.
Configure proactive alerts and capacity planning to prevent storage-related outages.

What's Next?¶

Memory Monitoring — Monitoring RAM and Swap Usage in Linux

You'll explore:

Understanding Linux memory management
Physical memory and swap usage
Monitoring memory consumption
Using free, vmstat, and related tools
Identifying memory-intensive processes
Troubleshooting memory issues
Production memory monitoring best practices

By the end of the lesson, you'll be able to monitor memory utilization, identify memory bottlenecks, troubleshoot out-of-memory conditions, and optimize memory usage in production Linux environments.