I actually am blown away by the reliability of hard drives. We've found that after 4 years, nearly 80% of hard drives are still working, and the median life is about 6 years: https://www.backblaze.com/blog/how-long-do-disk-drives-last/

Considering a 4 TB hard drive has to track 32,000,000,000 individual bits, allowing reading and writing repeatedly of each one, on platters that are spinning 120x per second, spaced a hair's width from their heads...I think it's actually incredible.

As for SSDs, we keep wishing that we could switch to them, but they're still 10x more expensive on a $/TB basis. That may change in the next few years, and if it does, we'll look forward to sharing data on SSD usage at scale as well.

Gleb (CEO, Backblaze)