skip all the gory details, their primary benefit to ReiserFS is their astounding speed. For example, searching a tree with trillions of items takes only a few dozen operations. For ReiserFS, storing metadata in the tree meant there was no limit to the number of files a directory could contain—unlike Ext2, which got bogged down for every file added.

But this had a price: high cpu usage. When your filesystem is competing for cpu cycles, you have a problem. In practice, ext2 was the fastest for normal use. Other filesystems added journaling which made them slower on a normal system (update data + journal). Of course, as CPU speed evolved, journaling was becoming faster.

Reiserfs on a 486 was unusable.