Although there are other file systems, the Extended File System (ext) is the one most commonly used with Linux. The current version is 4. The ext4 file system can support volumes with sizes up to 1 exabyte (10¹⁸ bytes or 1 billion gigabytes) and single files with sizes up to 16 terabytes. These sizes are extremely large, indicating that there will not be a need for an update to ext anytime soon.

The first two versions of ext did not support journaling; ext3 was the first to support journaling. Ext3 and ext4 support three specific types of journaling. The most secure and safe level is called journal. With the journal level, metadata and file contents are written to the journal before being written to the main file system. The next level, slightly less secure than journal, is called ordered. With the ordered level, only metadata is written to the journal; however, changes to files are not journaled until they have been committed to the disk. Finally, the least secure level is writeback. With the writeback level, only metadata is written to the journal, and it might be written to the journal before or after it is actually committed. Ext4 added checksums in the journal to prevent errors.

The Reiser File System (ReiserFS) was first introduced as a part of the Linux kernel version 2.4.1. ReiserFS has always supported journaling. ReiserFS performs very well when the hard drive has a large number of smaller files. In fact, tests have shown that when you are dealing with files that are under 4 KB in size, ReiserFS outperforms ext2 and ext3.

The Berkeley Fast File System is also known as the UNIX File System. It was developed at University of California, Berkeley specifically for use with Linux. Berkeley uses a bitmap to track free clusters, indicating which clusters are available and which are not.