E4RAT - Improving Startup Times by Physical Block Reallocation

Table of contents

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.

To view the entire boot chart just click on the picture.