e4rat is said to increase the boot speed on ext4 filesystems. However, it requires the ureadahead component of Ubuntu to be disabled. Will it really make my computer start faster and is it safe to try?
I tried it this weekend on a 12.04 (on a computer with a 1TB HDD and which has been upgraded 4 times without re-installation) and found it took 17 seconds off my boot process with no ill effects noticed.
It took me about 30mins to complete the process and I am happy with it so far.
It does seem to speed up the boot/login process quite a bit, but it's far less polished then ureadahead -- you have to manually go through logging the startup, dropping to recovery, reallocating the files, and messing with grub every time you want to update the cache. It also breaks the plymouth boot screen. I'm going to try tweaking ureadahead instead.
Is it safe? I can't guarantee anything, but it seems quite safe to me.