Difference between ext2,ext3,ext4

EXT2 to EXT3 and EXT3 to EXT4 Converting without data erase

Difference between ext2, ext3 and ext4 file system-

EXT-2	EXT-3	EXT-4
Ext2 stands for second extended file system.	Ext3 stands for third extended file system.	Ext4 stands for fourth extended file system.
It was introduced in 1993. Developed by Rémy Card.	It was introduced in 2001. Developed by Stephen Tweedie.	It was introduced in 2008.
This was developed to overcome the limitation of the original ext file system.	Starting from Linux Kernel 2.4.15 ext3 was available.	Starting from Linux Kernel 2.6.19 ext4 was available.
Ext2 does not have journaling feature.	The main benefit of ext3 is that it allows journaling.	Supports huge individual file size and overall file system size.
Maximum individual file size can be from 16 GB to 2 TB	Maximum individual file size can be from 16 GB to 2 TB	Maximum individual file size can be from 16 GB to 16 TB
Overall ext2 file system size can be from 2 TB to 32 TB	Overall ext3 file system size can be from 2 TB to 32 TB	Overall maximum ext4 file system size is 1 EB (exabyte). 1 EB = 1024 PB (petabyte). 1 PB = 1024 TB (terabyte).

EXT2 to EXT3 and EXT3 to EXT4 Converting without data erase- Ext2 to ext3 file conversation
# tune2fs ­j /dev/sda5

Ext3 to ext4 file system conversation
# tune2fs ­O dir_index,uninit_bg,extents /dev/sda5

Ext2 to ext4 file system conversation
# tune2fs ­O dir_index,uninit_bg,has_journal /dev/sda5

Ext3 to ext2 file system back conversation
 # tune2fs ­O ^has_journal /dev/sda5