Using just fio without kernel tracing, you run the risk of testing the filesystem instead of the storage medium. You could use fio to fabricate I/O operations,

Using just fio without kernel tracing, you run the risk of testing the filesystem instead of the storage medium. You could use fio to fabricate I/O operations, but the measurements coming from tracing are more trustworthy than the userspace measurements fio makes (unless fio does some in-kernel measurements I don't know about).