https://zielmicha.com/random-read-performance/

bench.py

import random, time

f = open('/dev/sda', 'rb')
L = 1000 ** 4 * 2

bs = 4096

while bs <= 1024 * 1024 * 128:
    count = 0
    start = time.time()
    while time.time() - start < 30:
        f.seek(random.randrange(0, L, bs), 0)
        f.read(bs)
        count += 1
    took = time.time() - start
    size = bs * count
    print 'bs=%dk' % (bs / 1024), 'read=%d' % count, 'size=%.1f MB' % (size / 1024**2), 'speed=%.1f MB/s' % (size / took / 1024**2)

    bs *= 2