a normalized value, which ranges from 1 to 253 (with 1 representing the worst case and 253 representing the best) and a worst value, which represents the lowest recorded normalized value. The initial default value of attributes is 100 but can vary between manufacturer.
SMART 187: Reported_Uncorrect:
Backblaze uses this one. Number 187 reports the number of reads that could not be corrected using hardware ECC. Drives with zero uncorrectable errors hardly ever fail. This is one of the SMART stats we use to determine hard drive failure; once SMART 187 goes above zero, we schedule the drive for replacement.
This first chart shows the failure rates by number of errors. Because this is one of the attributes we use to decide whether a drive has failed, there has to be a strong correlation: