Backblaze has been storing and analyzing data on its storage servers and drive failure rates. They have open sourced the design of their storage servers and provided instructions on how to build one. They currently use storage servers from Backblaze, Dell, and Supermicro. They have divided their storage servers into six cohorts called Backblaze Vaults. Each Vault is made up of a specific cohort of storage servers. The average age of the drives in the Backblaze 3.0 Vaults is around seven years, while the Backblaze 6.0 Vaults have much younger drives. Surprisingly, the failure rates of the different Vault cohorts do not seem to be correlated with the age of the drives. Further analysis will be conducted to understand these failure rates better.
https://www.backblaze.com/blog/the-drive-stats-of-backblaze-storage-pods/