From the ever so helpful people at Backblaze:
For the last few years we’ve used the following five SMART stats as a means of helping determine if a drive is going to fail.
Attribute Description SMART 5 Reallocated Sectors Count SMART 187 Reported Uncorrectable Errors SMART 188 Command Timeout SMART 197 Current Pending Sector Count SMART 198 Uncorrectable Sector Count
When the RAW value for one of these five attributes is greater than zero, we have a reason to investigate. We also monitor RAID array status, Backblaze Vault array status and other Backblaze internal logs to identify potential drive problems. These tools generally only report exceptions, so on any given day the number of investigations is manageable even though we have nearly 70,000 drives.