So item #3 includes the following errors:
From experience, we have found the following 5 SMART metrics indicate impending disk drive failure:
- SMART 5 – Reallocated_Sector_Count.
- SMART 187 – Reported_Uncorrectable_Errors.
- SMART 188 – Command_Timeout.
- SMART 197 – Current_Pending_Sector_Count.
- SMART 198 – Offline_Uncorrectable
https://www.backblaze.com/blog/hard-drive-smart-stats/
Basically they replace a drive once it shows 1 un^or^ec^abl^ error.
I didn't see how many of their drives failed under items #1, #2 or #3. If a drive continues to read and write data yet it is replaced based on a SMART stat, I dont think that data is terribly useful for anyone else who doesn't use those stats as a predictor of failure.