Backblaze is a company that offers cloud storage space and therefore operates a large amount of storage arrays.

In their own words:

As of December 31, 2018, we had 106,919 spinning hard drives. 

https://www.backblaze.com/blog/hard-drive-stats-for-2018/

This large amount of spinning disks means that there are also failing drives that stop spinning once every while. Backblaze saw the need to take note about what hard-drive series fails more of less often and started to generate a yearly report on the reliability of these hard drives.

Yesterday they published their report for 2018 – if you got storage requirements or if you are in the market to purchase storage space for your operation – it probably is very helpful to take a look at the report.