dt is a generic data test program used to verify proper operation of
peripherals, file systems, device drivers, or any data stream supported
by the operating system. In its simplest mode of operation, dt writes
and then verifies its default data pattern, then displays performance
statistics and other test parameters before exiting. Since verification
of data is performed, dt can be thought of as a generic diagnostic tool.

dt has been used to successfully test disks, tapes, serial lines,
parallel lines, pipes, and memory mapped files. In fact, dt can be used
for any device that allows the standard open, read, write, and close
system calls.  Special support is necessary for some devices, such as
serial lines, for setting up the speed, parity, data bits, etc.

WWW: http://home.comcast.net/~SCSIguy/SCSI_FAQ/RMiller_Tools/dt.html