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Comment by yason | Hacker News Reader

AFAIK, ureadahead just keeps track of which files/blocks are touched during bootup/startx and pre-reads them into a cache at the very beginning of the boot sequence so you will effectively boot from cache.

This still requires seeking to several semi-random areas of the disk while prereading which e4rat is fixing by physically moving the needed blocks adjacent to eachother.

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Since ureadahead looks at blocks and not files, it has a potential speed advantage if the boot process is opening some large files but not reading them in full.

Edit: except the ureadahead packfile only points to the blocks and files, it does not provide a way to inline them. So e4rat is almost certainly faster. It's a shame it is ext4 specific.

Apparently Scott James Remnant, the ureadahead developer, considered feeding the collected info to a defragmenter: http://ubuntuforums.org/showthread.php?t=1434502 ; this would be nice, as it means a single package is responsible for the feature, and filesystems perform to the best of their ability whether or not they have ext4-like fine-grained control of defragmentation.

So it sounds like the filesystem-reorganizing features of e4eat (but not the profiling features) would be complementary to ureadahead.

For some reason, I had the idea that ureadahead's pack files actually contained the contents of the blocks that needed to be read during boot, turning readahead into a sequential operation. After reading the manpage today, I see that I was mistaken.

It would be nice if someone installed e4rat on Ubuntu (with ureadahead) and reported the performance.

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