To build, simply run make in the thrash directory:
$ make
To install thrash into /usr/local/sbin/, type, become root with:
$ su -
.....
cd back into the thrash directory, and install with:
make install


That should be it, the thrash executable will be in 
/usr/local/sbin/ and the man page will be in /usr/share/man/man1/.

You will need to be superuser to use thrash. 

Typical usage for a short test:
# thrash -c 1000 -b 4096 /dev/sda

My main drive (74 GB, SATA Raptor, 10,000 rpm) generates this output:
Device size 72613056 Kbytes, using O_DIRECT reads. Not flushing /dev/sda.
Will stop on read errors.
1000 random reads of size 4096, in 7 secs, 660 msecs
Read 4096000 bytes in 7.660 seconds, 534726 bytes per second, 130.548 seeks/reads per second.

Parallel read test:
# for i in 1 2 3 4 5 6 7 8 ; do ./thrash -r $RANDOM -c 500 -b 4096 /dev/sda > /tmp/output_$i & done
wait for it to finish then:
# cat /tmp/output_* | grep "per second"
Which gave a total 160 reads per second, faster because of request reordering. 

