The hdparm tool is available out of the box in most Linux distributions.

hdparm -tT /dev/sda1

result:

/dev/sda1:
 Timing cached reads:   20780 MB in  1.99 seconds = 10416.77 MB/sec
 Timing buffered disk reads: 620 MB in  3.01 seconds = 206.13 MB/sec

There are multiple things to understand here in the above hdparm results. The -t Option will show you the speed of reading from the cache buffer (That's why it's much much higher).

The -T option will show you the speed of reading without precached buffer(which from the above output is low 206.13 MB/sec as shown above.)

The hdparm output shows you both the cached reads and disk reads separately.