Here are two freeware portable utilities which will help you benchmark & monitor your hard disk & USB Drives.

With the help of CrystalDiskMark utility, you can benchmark and test your hard disk & USB drives read & write speeds.

CrystalDiskInfo is a HDD/SSD utility software which supports S.M.A.R.T.

It supports a part of external USB disks  helps in Monitoring the health status and temperatures. It throws up a lot of information about your drives.

Also see HD Tune.

If you have liked this post, you might want to check out some more, on topics like Freeware, Hard Disk, Hardware.