Terminal method
hdparm is a good place to start.
sudo hdparm -Tt /dev/sda
/dev/sda:
Timing cached reads: 12540 MB in 2.00 seconds = 6277.67 MB/sec
Timing buffered disk reads: 234 MB in 3.00 seconds = 77.98 MB/sec
sudo hdparm -v /dev/sda will give information as well.
dd will give you information on write speed.
If the drive doesn't have a file system (and only then), use of=/dev/sda.
Otherwise, mount it on /tmp and write then delete the test output file.
dd if=/dev/zero of=/tmp/output bs=8k count=10k; rm -f /tmp/output
10240+0 records in
10240+0 records out
83886080 bytes (84 MB) copied, 1.08009 s, 77.7 MB/s
