Upgrading CentOS 5 to 5.6 is as simple as "yum update", and then reboot.
CentOS 5.6 / RedHat RHEL 5.6 has now the production ready Ext4 filesystem. To get this, simply run
# yum install e4fsprogs
Then you can create filesystem using
# mkfs -t ext4 /dev/sdc1
At the end of the above "mkfs", there is a message as below:
This filesystem will be automatically checked every 35 mounts or
180 days, whichever comes first. Use tune4fs -c or -i to override.
The utility "tune4fs" can also be used to convert ext3 filesystem into ext4.
To change the label of and ext4 partition, use 'e4label'.