I have about 20 ext hdds and the break/stop working within a year or two and I have to replace them. Some of them are USB 2.0, some Firewire and some are SATA. Before I built my computer, I only had USB 2.0 and Firewire. Half of the ext hdds contain original and the other half contain back-up copies. I rarely turn on an ext hdd that contains my back-ups, only to add some files, but they break quickly also.
The int hdd never breaks and it gets the most use. It has my programs on it and a lot of files on it. It's also the drive that I use to download/install programs and files and run cleaning and anti-virus/malware programs on it, defrag often, etc.
Is there an explanation why my int hdd never break but my ext hdds break quickly? 99% of them contain video files that I watch.