What Is ext3 (Third Extended File System)?

April 8, 2024

The Third Extended File System (ext3) is a journaling file system that was widely used by the Linux kernel. It was designed to be an extension of the Second Extended File System (ext2), providing backward compatibility while adding important new features. One of the most significant additions was the introduction of journaling, which greatly improved the reliability and integrity of the file system, especially in situations where the system might not be shut down cleanly, such as during a power outage or system crash.

ext3 Features

Here’s a closer look at some of ext3 primary features:


The most important feature of ext3 is its journaling capability, which greatly improves the file system's reliability and reduces the time required for recovery after a crash. In a journaling file system, changes are first recorded in a dedicated area called a journal before they are applied to the main file system. This process ensures that even in the event of a system failure, the file system can be quickly brought back to a consistent state by replaying or ignoring incomplete transactions recorded in the journal.

Online File System Growth

ext3 supports resizing the file system while it is mounted and in use, a feature known as online file system growth. This is particularly useful for system administrators who need to increase the storage capacity without downtime.

Htree Indexing for Directories

To improve the performance of operations in directories containing a large number of files, ext3 implements Htree indexing, a method that uses a hashed B-tree structure to index directory entries. This mechanism reduces the time required to find files in large directories, enhancing overall system performance.

Backward Compatibility with ext2

ext3 is backward compatible with ext2, meaning that an ext3 file system can be mounted and used as an ext2 file system. This feature facilitates easy upgrades from ext2 to ext3 without the need for data migration. Conversely, ext3 file systems can be mounted as ext2, albeit without journaling support.

Support for Large Files and File Systems

ext3 can support files up to 2TB in size and file systems up to 32TB. This was a significant improvement over ext2 and met the requirements of most applications and systems at the time of its development.

Access Control Lists (ACLs) and Extended Attributes

ext3 supports Access Control Lists (ACLs), which provide a more flexible permission mechanism than the traditional UNIX file permissions. Additionally, extended attributes allow users and applications to associate additional metadata with files and directories beyond the standard file attributes.

Journaling Modes

ext3 offers different journaling modes that allow users to balance between performance and data integrity. These modes include:

  • Journal. Both data and metadata are journaled, providing the highest level of integrity but potentially impacting performance.
  • Ordered. Only metadata is journaled, but data blocks are written before the associated metadata is committed to the journal. This is the default mode, providing a good balance between performance and reliability.
  • Writeback. Only metadata is journaled, and there is no guarantee that data blocks are written before metadata. This mode offers the best performance but the least data integrity assurance.

ext3 Advantages and Disadvantages

The ext3 file system introduced significant improvements in file system technology compared to its predecessor, ext2. However, it came with a set of drawbacks that revealed themselves over time, such as fragmentation, performance issues, and lack of support for very large storage volumes. Below we examine these advantages and disadvantages of ext3.


Here are the advantages of ext3:

  • Improved reliability. The journaling feature significantly enhances file system reliability by keeping a record of changes that are about to be made. In case of a system crash or power failure, this allows the file system to recover quickly by replaying changes from this journal, thus minimizing the risk of data corruption.
  • Faster recovery times. Unlike ext2, which could require extensive file system checks (fsck) after a crash, ext3's journaling reduces the need for such checks, leading to much faster recovery times.
  • Ease of upgrade. One of the major advantages of ext3 was its backward compatibility with ext2. This allowed users to upgrade their file systems from ext2 to ext3 without needing to format or migrate data, which was a significant convenience and time saver.
  • Flexibility. Systems could mount an ext3 file system as ext2 if needed (albeit without journaling benefits), providing flexibility in how the file system was used and maintained.
  • Support for large volumes and files. ext3 supported file systems up to 32TB and file sizes up to 2TB, which was sufficient to address the needs of users with large databases and files at the time.
  • Improved data integrity. The journaling modes (journal, ordered, and writeback) offered choices between performance and data integrity levels, allowing administrators to choose the most appropriate mode for their needs. This flexibility helped in optimizing systems based on the priority of data integrity versus performance.
  • Access Control Lists (ACLs) and extended attributes. Support for ACLs provided more granular control over file permissions, enhancing security and collaboration capabilities. Extended attributes allow for storing additional metadata, which is beneficial for certain applications and services.


Here is a list of drawbacks of ext3, especially when compared with newer systems:

  • Fragmentation. ext3 can suffer from fragmentation over time, especially in environments with a large number of small files or with file systems that are frequently written to and deleted from. Fragmentation can degrade performance because it increases the time it takes to read or write files, as the heads on a hard disk drive need to move to different locations to access file fragments.
  • Limited journaling flexibility. While ext3 introduced journaling, which significantly improved data integrity and recovery time after crashes, its implementation is not as flexible or efficient as in newer file systems. For example, ext4's journaling is more efficient and offers a delayed allocation feature that improves performance and reduces fragmentation.
  • File size and file system size limitations. ext3 supports file sizes up to 2TB and file system sizes up to 32TB, which, while sufficient at the time of its development, are limiting for modern applications that deal with larger datasets. Newer file systems like ext4 and Btrfs support much larger files and file systems, making them more suitable for large-scale storage needs.
  • Lack of built-in support for snapshots and compression. ext3 does not offer built-in support for snapshots or data compression, features that are increasingly important for backup, data recovery, and efficient storage management. Snapshots record the file system state at a particular point in time whereas compression significantly reduces the amount of disk space used. Both features are available in newer file systems like Btrfs and ZFS.
  • Single block group size limitation. The size of a block group in ext3 is fixed, limiting the maximum number of blocks and, consequently, the total size of the file system. This architecture impacts the scalability of the file system, making it less suitable for very large storage volumes compared to newer solutions.
  • Efficiency in handling large directories. While Htree indexing improved the efficiency of handling large directories compared to ext2, ext3 can still experience performance degradation when managing directories with tens of thousands of files or more. Newer file systems have further optimized directory handling and indexing, reducing lookup times and improving overall performance in these scenarios.
  • Delayed allocation is not supported. Delayed allocation, a feature introduced with ext4, allows the file system to delay the allocation of disk blocks until the data is written to the disk. This improves performance and reduces fragmentation but is not available in ext3.

How to Create ext3 File System?

Creating an ext3 file system involves formatting a partition with the ext3 file system type. This process can be performed on any block device, such as hard drives, SSDs, or partitioned space, and is commonly executed through the command line in Linux. Before proceeding, ensure that any important data on the partition to be formatted is backed up, as this process will erase existing data.

Here's how to create an ext3 file system step by step:

Step 1: Identify the Partition

First, you need to identify the block device you want to format with the ext3 file system. You can list all available block devices and their partitions using the lsblk or fdisk -l command.



sudo fdisk -l

Look for the device identifier that corresponds to the partition you wish to format, such as /dev/sdb1.

Step 2: Unmount the Partition (If Necessary)

If the partition is mounted, you must unmount it before formatting. Use the umount command followed by the device identifier:

sudo umount /dev/sdb1

If the partition is not mounted, you can skip this step.

Step 3: Create the ext3 File System

To format the partition with the ext3 file system, use the mkfs.ext3 command followed by the device identifier:

sudo mkfs.ext3 /dev/sdb1

This command will create an ext3 file system on the specified partition. You can add the -L option to assign a label to the file system:

sudo mkfs.ext3 -L MyExt3Partition /dev/sdb1

Step 4: Mount the File System

After formatting, you can mount the new ext3 file system to a directory in your file system hierarchy. First, create a mount point if it does not already exist:

sudo mkdir /mnt/myext3

Then, mount the ext3 file system to the newly created directory:

sudo mount /dev/sdb1 /mnt/myext3

Step 5: Verify the File System

Finally, you can verify that the file system is mounted and check its type using the df or mount command:

df -Th /mnt/myext3


mount | grep /mnt/myext3

These commands will show information about the mounted file system, including its type (ext3 in this case).

Important Considerations

  • Data loss. Formatting a partition will erase all existing data on it. Ensure you have backups before proceeding.
  • Device identifier. Be absolutely certain of the partition's device identifier (/dev/sdb1 in the example). Formatting the wrong partition can result in data loss.
  • Root privileges. These commands require root privileges, so they are prefixed with sudo. Depending on your system setup, you may need to enter your password.

Anastazija is an experienced content writer with knowledge and passion for cloud computing, information technology, and online security. At phoenixNAP, she focuses on answering burning questions about ensuring data robustness and security for all participants in the digital landscape.