Generally speaking, you can rely on your hard drive for three to five years on average. The online backup company BackBlaze

analysed the failure rates of their 25,000 running hard drives. They found that 90% of hard drives survive for three years, and

80% for four years. Those hard drives were running 24/7, so I presume a external hard drive will last much longer, if used

less.    The standard hard drive warranty runs about 3 years.