Benchmarking a HDD using the Benchmark utility in "Disks" on Ubuntu 16.04
hdparm is a standard CLI for testing disk speed and the drives don't have to be mounted (when doing read tests).
$ sudo hdparm -tT /dev/nvme0n1
/dev/nvme0n1:
Timing cached reads: 20760 MB in 1.99 seconds = 10414.33 MB/sec
Timing buffered disk reads: 5104 MB in 3.00 seconds = 1701.12 MB/sec
$ sudo hdparm -tT /dev/sdb
/dev/sdb:
Timing cached reads: 18822 MB in 1.99 seconds = 9442.74 MB/sec
Timing buffered disk reads: 80 MB in 3.08 seconds = 26.01 MB/sec
The first drive is an SSD and the second drive is a USB pen drive.