Fakeiops is a project mainly written in C, it's free.
an LD_PRELOAD library for simulating storage systems with various IOPS
FakeIOPS - an LD_PRELOAD library for simulating storage systems with various IOPS
% gcc -fPIC -Wall -g -O -shared fakeiops.c -ldl -o fakeiops.so
% LD_PRELOAD=/path-to/fakeiops.so FAKEIOPS=1000 ./testprog