What is the Ext4?

Answer 1

Ext4 (fourth extended filesystem) is file system used in Linux and it was introduced as the successor to ext3. Ext 4 is a deeper improvement over ext3, many of them was originally developed by Cluster file system from 2003 to 2006, aiming to extend storage limitation and improving performance. But some developer of Linux kernel did not accept extensions to ext3 for the reason of stability. They advised to fork the ext3's source code and rename it as ext4. Then the ext3 filesystem maintainer announced the new plan of ext4 in 2006. In the year 2008, the ext4 file system was released, which is contained in Linux 2.6.28. Ext4 filesystem is an improved design with better performance, reliability and features. The follow part talks about several main features of ext4 file system.

• Backward compatibility. Ext4 filesystem is backward compatible with ext3 and ext2. Ext 3 filesystem can be migrated to ext4 with the help of several commands in read-only mode. Thus you can convert ext3 to ext4 without reformatting or reinstalling operating system. But you cannot go back to ext3 once it is has upgraded to ext4.
• Journal checksumming. Journal is one of the most used parts of the disk, which makes block that form part of it more prone to hardware failure. Sine recovering from corrupted journal can cause massive corruption, ext4 checksums the journal data to make sure whether journal blocks are corrupted. Besides, it is able to safely avoid disk I/O waiting during journaling, improving performance.
• Larger filesystem / file size. Ext3 supports 16TB maximum filesystem size and 2TB maximum file system, while ext4 can support up to 1EB (1EB = 1024PB = 1024*1024TB =1024*1024 GB) file system size and 16TB of maximum file size, as ext4 adds 48-bit block addressing. 1EB = 1024PB = 1024*1024TB =1024*1024 GB