I found a server last week that was having severe issues with disk I/O to the point where most operations were taking many minutes to complete. The server wasn’t under much load, but a quick run of dmesg threw quite a bit of these lines out onto the screen: EXT3-fs warning (device sda5): ext3_dx_add_entry: Directory index full! After a thorough amount of searching, I couldn’t find out what the error actually meant.