The offsite backup company Backblaze (who I fully endorse by the way) recently revealed some very interesting statistics about their hard disks.
You see luckily for us Backblaze use over 25,000 domestic quality drives to backup all our data and this gives them a unique insight into the life and performance of drives that you and I might purchase ourselves.
In a process that is likely akin to painting the Sydney harbor bridge (never ending) they are constantly monitoring and replacing drives and as such have managed to amass the following stats.
Your drive has a 70% of living until its 4 years old (don’t feel too bad, computers age like dogs) but anything beyond that it falls off dramatically to around a 50/50 chance that it will ever see its 5th birthday.
So its very important to get a Time Machine and/or a Backblaze backup setup. If you have one, check it often. If you don’t have a backup I would highly recommend getting one in place.
Have a read of the article, its very interesting.