The Ext4 stands for the fourth extended filesystem. It's a journaling file system for Linux, developed as the successor to ext3. It was introduced in 2008. It was released as a series of backward-compatible extensions to ext3, many of them originally developed by Cluster File Systems for the Lustre file system between 2003 and 2006, meant to extend storage limits and add other performance improvements. Ext4 modifies important data structures of the filesystem such as the ones destined to store the file data. The result is a filesystem with an improved design, better performance, reliability, and features.
Support for the ext4 file system has been available from the Linux kernel version 2.6.19 onwards and was officially declared stable in the Linux kernel version 2.6.28. All the latest versions of distributions like Ubuntu, Fedora etc. include the ext4 file system.
ext4's extent allocation does wonder when you use BitTorrent. When a BT client pre-allocates a large chunk (say, when you're downloading a DVD iso) of the disk to avoid fragmentation, on ext4 it's near instantaneous, while on ext3 it can take dozens of seconds.
Features
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The ext4 filesystem can support volumes with sizes up to 1 exbibyte (EiB) and single files with sizes up to 16 tebibytes (TiB) with the standard 4 KiB block size.
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Ext4 uses a performance technique called allocate-on-flush, also known as delayed allocation.
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Extents replace the traditional block mapping scheme used by ext2 and ext3.
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A single extent in ext4 can map up to 128 MiB of contiguous space with a 4 KiB block size.
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Ext4 does not limit the number of subdirectories in a single directory, except by the inherent size limit of the directory itself.
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The ext4 is backward-compatible with ext3 and ext2, making it possible to mount ext3 and ext2 as ext4.
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Ext4 uses checksums in the journal to improve reliability since the journal is one of the most used files of the disk.
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Ext4 can pre-allocate on-disk space for a file. To do this on most file systems, zeroes would be written to the file when created.
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In ext4, a new system call in the Linux kernel can be used. The allocated space would be guaranteed and likely contiguous.
Let’s see the advantages and disadvantages of EXT4 partition
Advantages
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You can use different disks/LUNs and have better performance. This can increase the performance of the databases as you can have the transaction log on storage and the data files on another. Similar for disk I/O intensive web applications.
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You can use different mount options (that increase the security or that affect the performance or stability in a more granular way).
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You manage the space separately. So you can have a nasty application that fills the space that is not affecting other applications.
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Fragmentation of one partition is independent of the other.
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You can snapshot, mount, umount, format, defragment, monitor for the performance of file systems independently.
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You can have encryption on specific volumes.
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You can mount volumes on demand.
Disadvantages
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It increases the administration overhead.
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You will have greater chances to waste more disk space.
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You will have more incidents involving disk full.
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It is more difficult to create a consistent snapshot of an application running on different volumes.
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It uses slightly more resources.
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Depending on the volume type (MS-DOS label, LVM, btrfs...) you might not be able to easily allocate space from a volume by shrinking another.
You can share your experiences with us in the comment section. Thank you!
