What is ext4?

ext4 (short for “fourth extended filesystem”) is a type of file system that computers use to store and organize files on a hard drive or SSD. It’s the default system for most modern Linux distributions because it’s fast, reliable, and can handle very large storage devices.

Let's break it down

  • ext4: the name of the file system; “ext” means “extended” and the “4” shows it’s the fourth version.
  • File system: a set of rules that tells the computer how to keep track of where data is saved, like a digital filing cabinet.
  • Store and organize files: saving documents, pictures, programs, etc., and keeping them in a way the computer can find them quickly.
  • Hard drive or SSD: the physical devices where data lives.
  • Default for Linux: the one most Linux systems choose automatically because it works well out of the box.
  • Fast, reliable, large: it reads/writes quickly, doesn’t lose data easily, and works with very big disks.

Why does it matter?

If you use a Linux computer, ext4 determines how quickly your programs start, how safely your photos and documents are kept, and whether you can use very big storage devices without trouble. Understanding it helps you troubleshoot performance issues and choose the right storage setup.

Where is it used?

  • Desktop and laptop computers running Ubuntu, Fedora, Debian, and many other Linux distros.
  • Servers that host websites, databases, or cloud services on Linux.
  • Embedded devices like routers, smart TVs, and IoT gadgets that run a lightweight Linux OS.
  • External USB drives or SSDs formatted for Linux users who need a portable, compatible storage solution.

Good things about it

  • High performance: fast read/write speeds, especially with modern SSDs.
  • Strong reliability: journaling protects data from corruption after power loss.
  • Large capacity support: can manage volumes up to 1 exabyte and files up to 16 terabytes.
  • Compatibility: works out-of-the-box with almost all Linux distributions.
  • Features like extents, delayed allocation, and online defragmentation improve efficiency.

Not-so-good things

  • Limited support on non-Linux operating systems (Windows/macOS need extra tools to read/write).
  • No built-in encryption; you need separate tools (e.g., LUKS) for data security.
  • While robust, it lacks some advanced features found in newer file systems like Btrfs or ZFS (snapshots, built-in RAID).
  • May require manual tuning for optimal performance on very specific workloads (e.g., high-frequency small writes).