- Ext4 was released as a functionally complete and stable filesystem in Linux 2.6.28
- It's safe to use it in production environments.
- The ext4 or fourth extended filesystem is a journaling file system developed as the successor to ext3.
- Kernel 2.6.28, containing the ext4 filesystem, was finally released.
- The ext4 filesystem can support volumes with sizes up to 1 exabyte and files with sizes up to 16 terabytes.
- Extents are introduced to replace the traditional block mapping scheme used by ext2/3 filesystems.
- The ext4 filesystem is backward compatible with ext3 and ext2, making it possible to mount ext3 and ext2 filesystems as ext4.
- In ext3 the number of subdirectories that a directory can contain is limited to 32,000. This limit has been raised to 64,000 in ext4.
- Ext4 uses checksums in the journal to improve reliability, since the journal is one of the most used files of the disk.
- In ext4, unallocated block groups and sections of the inode table are marked as such. This enables e2fsck to skip them entirely on a check and greatly reduce the time it takes to check a file system of the size ext4 is built to support.
- Ext4 allocates multiple blocks for a file in single operation, which reduces fragmentation by attempting to choose contiguous blocks on the disk.
- Right now there's not a stable version of grub that supports booting a kernel from a ext4 partition. It's recommended that you keep /boot in a ext3 partition.
- Ext4 will use the new data structures only on new data, the old structures will remain untouched and it will be possible to read/modify them when needed.