When you install CentOS, cPanel recommend using an ext filesystem ext2, ext3, or ext4. If you are using CentOS 5.x with the ext4 filesystem, you will need to download and install the package mentioned in the Red Hat documentation.

When you install Red Hat Enterprise Linux (RHEL), cPanel recommend that you use an ext filesystem (ext2, ext3, or ext4).If you use Red Hat 5.x with the ext4 filesystem, you will need to download and install the package mentioned in the Red Hat documentation

Ext2 File System

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 File System

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. This allows it to be more robust in preventing file corruption, particularly when write processes are interrupted unexpectedly.
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

The ext3 filesystem provides three options.

These are as follows:

writeback – greater speed at the price of limited data integrity. Allows old data to show up in files after a crash and relies on kernel’s standard writebacks to flush buffers.

ordered -  that the data is consistent with the file system; recently-written files will never show up with garbage contents after a crash at the cost of some speed.

journal - Journals all data requiring greater journal space and reduced performance. The most secure data retention policy.

Ext4 File System

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”.

Please use this link to convert file systems to ext2 to ext3 or ext4.

http://www.thegeekstuff.com/2011/05/ext2-ext3-ext4/