http://www-106.ibm.com/developerworks/library/l-fs.html
Small file performance
So, how does one go about making the filesystem more accommodating? Namesys has decided to focus on one aspect of the filesystem, at least initially -- small file performance. In general, filesystems like ext2 and ufs don't do very well in this area, often forcing developers to turn to databases or special organizational hacks to get the kind of performance they need. Over time, this kind of "I'll code around the problem" approach encourages code bloat and lots of incompatible special-purpose APIs, which isn't a good thing.
Here's an example of how ext2 can tend to encourage this kind of programming. ext2 is good at storing lots of twenty-plus k files, but isn't an ideal technology for storing 2,000 50-byte files. Not only does performance drop significantly when ext2 has to deal with extremely small files, but storage efficiency drops as well, since ext2 allocates space in either one or four k chunks (configurable when the filesystem is created).
Now, conventional wisdom would say that you aren't supposed to store that many ridiculously small files on a filesystem. Instead, they should be stored in some kind of database that runs above the filesystem. In reply, Hans Reiser would point out that whenever you need to build a layer on top of the filesystem, it means that the filesystem isn't meeting your needs. If the filesystem met your needs, then you could avoid using a special-purpose solution in the first place. You would thus save development time and eliminate the code bloat that you would have created by hand-rolling your own proprietary storage or caching mechanism, interfacing with a database library, etc.
Well, that's the theory. But how good is ReiserFS' small file performance in practice? Amazingly good. In fact, ReiserFS is around eight to fifteen times faster than ext2 when handling files smaller than one k in size! Even better, these performance improvements don't come at the expense of performance for other file types. In general, ReiserFS outperforms ext2 in nearly every area, but really shines when it comes to handling small files.
