usb-storage or sata/libata driven) devices.
iodepth=x For async io, allow 'x' ios in flight
overwrite=x If 'x', layout a write file first.
+ nrfiles=x Spread io load over 'x' number of files per job,
+ if possible.
prio=x Run io at prio X, 0-7 is the kernel allowed range
prioclass=x Run io at prio class X
bs=x Use 'x' for thread blocksize. May include k/m postfix.
bwavgtime=x Average bandwidth stats over an x msec window.
create_serialize=x If 'x', serialize file creation.
create_fsync=x If 'x', run fsync() after file creation.
+ unlink If set, unlink files when done.
end_fsync=x If 'x', run fsync() after end-of-job.
loops=x Run the job 'x' number of times.
verify=x If 'x' == md5, use md5 for verifies. If 'x' == crc32,