What is the differences between ext2 ext3 and ext4 file system in Linux?

Answer 1

Ext3 is a tiny bit slower than ext2 is, but it holds tremendous advantages. There is really only one difference between ext2 and ext3, and that is that ext3 uses a journal to prevent filesystem corruption in the case of an unclean shutdown (ie. before the filesystem is synced to disk). That makes ext3 a bit slower than ext2 since all metadata changes are written to the journal, and then flushed to disk, but on the other hand you don't risk having the entire filesystem destroyed at power failure or if an unwitted person turns the computer off uncleanly. You don't have to check the filesystem after an unclean shutdown either. Ext3 has three levels of journalling. Metadata (ie. internal filesystem structures) are always journalled, so that the filesystem itself is never corrupted. How ordinary data is written to the file system is controllable, though. The default option is the "ordered" mode, which causes file contents to be written to the filesystem before metadata is even committed to the journal. The highest reliable mode is called the "journal" mode, which causes file data to be committed to the journal before it is flushed to its final place, like the metadata. The least reliable mode, but rumoured to be the fastest, is called the "writeback" mode, which makes no promises at all regarding the consistency of file data. Only metadata is output reliably in writeback mode. So as for anything else, it's mainly a matter of priority. If you don't want ultimate speed, go with ext3. If you need the highest speed that is theoratically aquirable though, then go with ext2. For that to be effective you'll probably need a really advanced hard drive controller, though.

Answer 2

The Linux ext2 filesystem gets its performance from having an asynchronous mount. You can mount FreeBSD UFS filesystems as asynchronous but this is very dangerous and no seasoned Unix admin would do this. It's amazing that Linux is designed this way by default. Often a hard carsh permanently damages a mount. FreeBSD or Solaris can sustain a very hard crash with only minor data loss, and the filesystem will be remountable with few problems. There are several new journaling filesystems in development for Linux that will fix some of these issues, but these will not be ready for the 2.4 release of Linux. The Microsoft FAT filesystem and the newer NTFS are both plagued by over 15 years of backwards compatability with the earliest of PC-based filesystems. These filesystems were not designed for today's demanding server applications, they weren't even designed with a multi-user OS or networking in mind!

Answer 3

The main benefits that ext4 has over ext3 are:

* faster timestamping * faster file system checking * journaling checksums * extents (basically automatic space allocation to avoid fragmentation)

Answer 4

Ext3 is a tiny bit slower than ext2 is, but it holds tremendous advantages.

There is really only one difference between ext2 and ext3, and that is that ext3 uses a journal to prevent filesystem corruption in the case of an unclean shutdown (ie. before the filesystem is synced to disk). That makes ext3 a bit slower than ext2 since all metadata changes are written to the journal, and then flushed to disk, but on the other hand you don't risk having the entire filesystem destroyed at power failure or if an unwitted person turns the computer off uncleanly. You don't have to check the filesystem after an unclean shutdown either.

Ext3 has three levels of journalling. Metadata (ie. internal filesystem structures) are always journalled, so that the filesystem itself is never corrupted. How ordinary data is written to the file system is controllable, though. The default option is the "ordered" mode, which causes file contents to be written to the filesystem before metadata is even committed to the journal. The highest reliable mode is called the "journal" mode, which causes file data to be committed to the journal before it is flushed to its final place, like the metadata. The least reliable mode, but rumoured to be the fastest, is called the "writeback" mode, which makes no promises at all regarding the consistency of file data. Only metadata is output reliably in writeback mode.

So as for anything else, it's mainly a matter of priority. If you don't want ultimate speed, go with ext3. If you need the highest speed that is theoratically aquirable though, then go with ext2. For that to be effective you'll probably need a really advanced hard drive controller, though.

Answer 5

Ext2

• Ext2 stands for second extended file system.
• It was introduced in 1993. Developed by Rémy Card.
• This was developed to overcome the limitation of the original ext file system.
• Ext2 does not have journaling feature.
• On flash drives, usb drives, ext2 is recommended, as it doesn't need to do the over head of journaling.
• Maximum individual file size can be from 16 GB to 2 TB
• Overall ext2 file system size can be from 2 TB to 32 TB

Ext3

• Ext3 stands for third extended file system.
• It was introduced in 2001. Developed by Stephen Tweedie.
• Starting from Linux Kernel 2.4.15 ext3 was available.
• The main benefit of ext3 is that it allows journaling.
• Journaling has a dedicated area in the file system, where all the changes are tracked. When the system crashes, the possibility of file system corruption is less because of journaling.
• Maximum individual file size can be from 16 GB to 2 TB
• Overall ext3 file system size can be from 2 TB to 32 TB
• There are three types of journaling available in ext3 file system.
  • Journal - Metadata and content are saved in the journal.
  • Ordered - Only metadata is saved in the journal. Metadata are journaled only after writing the content to disk. This is the default.
  • Writeback - Only metadata is saved in the journal. Metadata might be journaled either before or after the content is written to the disk.
• You can convert a ext2 file system to ext3 file system directly (without backup/restore).

Ext4

• Ext4 stands for fourth extended file system.
• It was introduced in 2008.
• Starting from Linux Kernel 2.6.19 ext4 was available.
• Supports huge individual file size and overall file system size.
• Maximum individual file size can be from 16 GB to 16 TB
• Overall maximum ext4 file system size is 1 EB (exabyte). 1 EB = 1024 PB (petabyte). 1 PB = 1024 TB (terabyte).
• Directory can contain a maximum of 64,000 subdirectories (as opposed to 32,000 in ext3)
• You can also mount an existing ext3 fs as ext4 fs (without having to upgrade it).
• Several other new features are introduced in ext4: multiblock allocation, delayed allocation, journal checksum. fast fsck, etc. All you need to know is that these new features have improved the performance and reliability of the filesystem when compared to ext3.
• In ext4, you also have the option of turning the journaling feature "off".