What is the difference between ext4 and ext3 in linux

Differences: 1. ext3 has 32,000 subdirectories, while ext4 has unlimited; 2. ext3 uses indirect block mapping, which is less efficient when operating large files. ext4 uses Extents, and each Extent is a set of consecutive Data block efficiency is high; 3. ext3 only allocates one data block at a time, while ext4 can allocate multiple at a time.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What is the difference between ext4 and ext3 in Linux

The file system is an organization method for files stored on storage devices such as disks. The Linux system can support a variety of currently popular file systems, including: EXT2, EXT3, EXT4, FAT, FAT32, etc. So what are the differences between ext3 and ext4 in Linux systems

1. Larger file systems and larger files

ext3: 16TB file system and maximum 2TB files;

ext4: 1EB file system and maximum 16TB file.

　2. Unlimited number of subdirectories

ext3: 32000 subdirectories;

ext4: unlimited number of subdirectories.

3. Extents

ext3: Using indirect block mapping, the efficiency is extremely low when operating large files. For example, for a 100MB file, a mapping table of 25,600 data blocks needs to be established in ext3.

Ext4: Introduces the concept of Extents. Each Extent is a set of continuous data blocks. The above file means that the file data is stored in the next 25,600 data blocks, which improves a lot of efficiency.

4. Multi-block allocation

The data block allocator of ext3 can only allocate one 4KB block at a time. To write a 100MB file, it needs to call the data block 25600 times. Allocator, and ext4's multiblock allocator supports allocating multiple data blocks in one call.

5. Delayed allocation

The data block allocation strategy of ext3 is to allocate as soon as possible, while ext4 delays allocation as much as possible until the file is written in the cache. Allocating data blocks and writing them to disk optimizes the allocation of data blocks throughout the file, which can significantly improve performance when paired with the first two features.

6. Inode related features

ext3:128byte;

ext4:256byte.

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