Ext Ext is for ‘Extended file system’. It was the first system created for Linux. Ext experienced 4 main revisions. It was presented in 1992 and was a massive update from Minix file system. It is far from perfect, so lots of Linux distributions no longer support Ext. Ext2 Ext2 does not support journaling. When it was presented, its modernity was that it supported extended file attributes and 2 terabyte drives. Ext2 absence of journal makes it comfortable to use on portable flash drives. However, more universal advanced file systems are available nowadays, like exFAT or FAT32. They are more usable with various OS and are comfortable. So, if you don’t need Ext2, it is better to pay attention to rather modern similar file systems. Ext3 Ext3 is similar to Ext2, but it includes journaling. It was created to be backwards connected with Ext2, so partitions between Ext2 and ext3 were able for conversion with no formatting. It is quite an old and usable version, but Ext4 is more common and stable. So, compared to Ext3, Ext4 is better in use. Ext4 Ext4 and Ext3 were created for compatibility reasons. The one has a built–in Ext4 file system, as Ext3, Ext2, and backwards. It was enhanced and involves fresh updates that reduced file fragmentation, made it possible to have larger files and sizes, and has a delayed allocation, which is profitable for flash memory duration. It is a basic or default version of the file system on Linux, nowadays. It had lots of updates and work put in it, so it is widely popular. BtrFS BtrFS usually stands for B–Tree File system, but is pronounced as ‘better’ or ‘butter’ FS. It was created by Oracle. This file system involves drivepool, automatic snapshot, transparent compression, and availability for online defragmentation. It was originally created to become an alternative to Ext series; also, it has something in common with the ReiserFS former default file system for Linux. BtrFS is often considered the next and better version of Ext4. We expect BtrFS to become equally popular in both segments of home and business usage, as it is continually developed and now is being tested. ReiserFS It was presented in 2001 as an alternative for Ext4. It was considered a great progress. It was so innovative that Ext4 was incapable of implementing most of its functions. ReiserFS soon was changed into Reiser4. Reiser4 was the improved version that corrected lots of features and was enhanced in 2004. However, after the incident in 2008 with main developer Hans Reiser, who went to prison, Reiser4 stopped progress. This file system is not included in the main list of Linux, and it is improbable for it to get there soon. BtrFS is a better solution. ZFS Oracle has the ownership for this file system, though initially, it was developed by Sun Microsystems for Solaris. ZFS is advanced, supports drive pool, automatic snapshot, and dynamic disk striping. After BtrFS was introduced, lots of these features became a default set. Every file in ZFS got a checksum, which helped to find and determine corrupted or damaged files. Due to the differences in licenses and ownership and legal moments, this file system cannot be included in the main list of Linux file system. However, it is still open-source, though it has Sun license, and it is supported by Linux distributions. Ubuntu, for example, still uses ZFS, especially in its 16/04 version. XFS XFS was created for Linux in 2001 by Silicon Graphics. It was made for the SGI IRX OS. It doesn’t support mounted snapshots and has delayed allocation for enhancing file fragmentation, and with such features, it is similar to Ext4. XFS recommended being effective with large files, but it doesn’t work well with small files, and the performance is worse than in many other file systems. So those who are trying to find something for their service that works with large files can consider XFS as an option. JFS JFS stands for ‘journaled file system’. It was originally developed by IBM in 1990, and after that, offered to Linux. It works well with both large and small files and has low CPU. The partitions in this file system can be resized; however, they cannot be shrunk. It was a good option for Linux, back in that day, but they chose the development of Ext series. It is still supported by most of Linux distribution, but initially, it was created for AIX. Ext4 is better to use, as it is more spread, tested, and supported. SWAP Swap is a special option for formatting a drive and creating a backup, but it is not a real file system. It is not structured as a system. It is only a space that keeps your data stored, and the size of data cannot be more than the volume of your RAM. SWAP option is also used during hibernation. In Windows, paging file has a similar mechanism, but it is in the main system partition, while Linux separates an empty partition for it and keeps it for a space to swap the data out. FAT32, exFAT, and NTFS FAT16, FAT32, and exFAT are Microsoft’s FAT file systems supported by Linux and used for formatting a drive. They have no journal, which makes them good for portable memory devices. They are default in every OS, whether it is Windows, macOS, or Linux. These file systems are great if you want to format an external drive using other OS. Nowadays, exFAT is the most appropriate version, as FAT32 is not so powerful. exFAT works with large files over 4 GB and partitions more than 8 GB, which is impossible for older (FAT32, FAT16) versions. NTFS is a newer and enhanced version of exFAT, with strengthened security and object–oriented applications. There is a wide variety of Linux file systems, but those mentioned here are the most well–known and widely used. Some of the file systems not mentioned here were created for different portable flash devices and other specific needs, so look for a file system to meet your needs.
Introduction A file system is a set of processes that controls how, where and when data is stored and retrieved from a storage device. An efficient file system is essential for everyday system processes. The Linux kernel supports various file systems, but the most commonly used is the ext4 file system. In this article, you will learn more about the development of Linux file systems and the main features of the ext4 system. 
Note: In Linux, everything is stored as a file (e.g., directories, printers, partitions, kernel data, etc.). That makes it all the more important to learn how the Linux file system works. Let’s take a closer look at the evolution of the Linux file system: The Minix file system supported the Minix operating system. It was first introduced in 1987 by Andrew S. Tanenbaum. The Minix operating system and its file system were mostly used for educational coding purposes. The performance of the file system was not up to standard at the time. Filename lengths were restricted to fourteen characters, and partitions were limited to 64MB. At the time, hard drives supported partitions up to 140MB. By 1992 Minix was mostly out of use due to lack of performance and development of the ext file system. The ext file system stands for “Extended File System”. It was the first file system designed to support the Linux kernel. Virtual File System (VFS) was used for the ext file system. Its primary purpose was to allow the Linux kernel to access the ext file system. The ext file system restricted filename lengths to 255 characters and supported partitions up to 2GB. While it managed to solve issues that the Minix file system had, it had one major flaw – timestamping. Unlike today where each Linux file has three timestamps (access timestamp, modified timestamp, and changed timestamp), the ext file system allowed only one timestamp per file. In January 1993, the ext2 file system was introduced. In time, all users switched from ext to ext2. Remi Card designed the ext2 file system and released it in January 1993, less than a year after introducing the ext file system. The ext2 file system enabled the retention of the internal structure while the file system functionalities extended. Data from files were kept in data blocks of the same length. The ext2 file system supported the maximum file size of 2TiB. Filename lengths were not limited in characters, but in bytes – 255 bytes. It did not support journaling. While this file system was largely used, it still had two major issues:
The ext2 system was mostly used until the early 2000s when the ext3 file system was introduced. It is occasionally used today for USB devices because it does not support the journaling system. Stephen Tweedie designed the ext3 file system (Third Extended File System). It launched in November 2001 with Linux kernel 2.4.15. It is still in use today. The ext3 file system is an improved version of ext2 file system. It supports a maximum file size of 2TiB and restricts maximum filename length to 255 bytes, like the ext2 file system. The improvement is reflected in journaling. The journaling system keeps a “journal” of all changes in the data structure that are yet to be commited. In case of power loss or system crash, logs stored via the journaling system return data in a manner of seconds, reducing the risk of corruption or data loss. The system writes the data in the correct areas of the file system when the log is updated. The Linux kernel supports three levels of journaling:
The ext4 file system is the default file system of the current Linux kernel. It was introduced in October 2008 with Linux kernel 2.6.28. The ext4 file system supports the maximum file size of 16TiB and restricts maximum filename lengths to 255 bytes. Let’s look at the main features of the ext4 file system. The ext4 file system supports backward compatibility with ext3 and ext2 file systems. An additional feature is the automatic mounting of the ext3 file system in ext3 mode by using an ext4 driver. The ext4 file system allocates storage blocks more efficiently prior to writing them to the disk. That improves read and write performance. The ext4 file system adds another 408 years to the timestamp and supports dates up to May 10, 2446. Timestamps are also measured faster, in nanoseconds. Outdated versions of the ext file system map all the blocks that correlate with each file. The process does not work when it comes to large files that require a high number of blocks. Extents have resolved the problem in the ext4 file system. Extents reduce the amount of metadata required to map each file’s blocks. The system saves the address of the first and last block corresponding to the large file. A block allocator searches for free blocks that can be used to write data to the disk. The ext4 file system uses multiple allocations that allow the allocation of multiple blocks per call. This reduces disk fragmentation. The delayed allocation feature allocates blocks only when the file is written to the disk. With this feature, cache memory is not filled with unnecessary data, and the performance of the system increases. Linux kernel version 2.6.23 supports an unlimited number of subdirectories. The ext4 file system introduced the HTree data structure to avoid drops in performance. The HTree data structure represents a specialized version of the B-tree. The ext4 file system uses the checksum option. This option was introduced to reduce the risk of file corruption. The journaling system is the most used part of the disk. When hardware failure occurs, the blocks become unusable and file corruption occurs. The checksum option constantly checks to see if a block is damaged. This process also improves performance because it shortens the journaling time. In an ext4 file system, undistributed groups of blocks and inode tables are marked. The time required to run the fsck command is significantly shortened because marked groups are skipped. It improves overall performance. Disk fragmentation leads to performance degradation, which was a significant issue with the ext2 and ext3 file systems. The ext4 file system supports the e4defrag tool that lets users defragment individual files or the complete file system. Although the ext4 file system is considered as the best file system for Linux distributions, there are a few limitations that should be considered in the further development of the system:
There are several alternatives to the ext4 file system. The Linux kernel supports all the alternatives listed below.
Note: To avoid issues, use alternative file systems under separate directories. XFS is a 64-bit file system that was first introduced in 1994 and built into the Linux kernel since 2001. It is the default file system for RedHat Linux. XFS supports a maximum file size of 8 EiB and restricts filename length to 255 bytes. It supports journaling, and like ext4, it saves the changes in a journal before changes are committed to the main file system. This reduces the possibility of file corruption. Data is structured in B+ trees, which provides efficient space allocation and therefore increased performance. This system’s main disadvantage is reflected in the difficult resizing process of an existing XFS file system. OpenZFS is a platform that combines file systems with volume managers. It was first introduced in 2013. OpenZFS supports a maximum file size of 16 EiB and limits the maximum filename length to 255 characters. Some of this system’s features are protection against data corruption, encryption, support for high storage capacities, copy-on-write, and RAID-Z. OpenZFS’ main disadvantage is the legal incompatibility between CDDL (OpenZFS) and GPL (Linux kernel) licenses. That is resolved by compiling and loading the ZFS code to the Linux kernel. Oracle designed BtrFS (stands for “B-tree file system”) and released it in 2009 with Linux kernel 2.6.29. BtrFS supports a maximum file size of 16 EiB and limits the maximum filename length to 255 characters. Some of the BtrFS’ features are online defragmentation, online block device addition and removal, RAID support, compression configurable per file or volume, file cloning, checksums, and the ability to handle swap files and swap partitions. Conclusion The Linux file system evolved for decades to gain its complexity and functionality. Each new functionality resolved an issue present in the outdated versions of the system. After reading this article, you should have a better understanding of the Linux file system and how it functions. Next, consider learning about data backups in our article Snapshot vs Backup. |
What is the default filesystem of Linux?
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