Oceanz, you misunderstand -- by low-level I mean low-level access to the filesystem, in other words instead of accessing it purely as files as most applications do, accessing it as blocks in the FS.
As I said it depends on your usage patterns as to whether a web-serving machine would require defragmenting -- a forum not using file uploads is unlikely to use temporary files, the *database server* OTOH may well perform this sort of operation.
Can you point to a specific web-server which defragments the filesystem during running?