Every now and then, you might want to create an ext4 filesystem on a block device spanning several terabytes, and this is almost always a really long process, taking up to several hours or even days.
There is a little known trick that can significantly reduce the amount of time needed to create ext4 filesystems:
mkfs.ext4 -E lazy_itable_init=1
The lazy_itable_init flag is default on newer versions of e2fsprogs, and the above snippet works on systems as old as Centos5.