e4rat ("Ext4 - Reducing Access Times") is a toolset to accelerate the boot
process as well as application startups. Through physical file realloction
e4rat eliminates both seek times and rotational delays. This leads to a high
disk transfer rate.

Placing files on disk in a sequentially ordered way allows to efficiently
read-ahead files in parallel to the program startup. The combination of
sequentially reading and a high cache hit rate may reduce the boot time by a
factor of three, as the example below shows.

e4rat is based on the online defragmentation ioctl EXT4_IOC_MOVE_EXT from the
Ext4 filesystem, which was introduced in Linux Kernel 2.6.31. Other filesystem
types and/or earlier versions of extended filesystems are not supported.