dbench is a filesystem benchmark that generates load patterns similar to those of the commercial Netbench benchmark, but without requiring a lab of Windows load generators to run. It is now considered a de-facto standard for generating load on the Linux VFS.

dbench produces only the filesystem load. It does all the same IO
calls that the smbd server in Samba would produce when confronted with
a netbench run. It does no networking calls.

You can get dbench from ftp://samba.org/pub/tridge/dbench/
You run it as "dbench N" where N is the number of clients to
simulate. It gives out three numbers like this (this is from a 144
client run on a quad xeon box):

Throughput 40.6701 MB/sec (NB=50.8376 MB/sec 406.701 MBit/sec)

More details... http://samba.org/ftp/tridge/dbench/README