Often they are not, but there are other fields that are more informative. UNC) (used only by some vendors): the count of read errors that could not be recovered automatically using ECC (see also 195/C3).

187 (0xBB), Reported Uncorrect (a.k.a.Often this is pretty redundant with 0x05 and 198/0xC6. 196 (0xC4), Reallocation Event Count: counts the attempts at reallocation - both successful and failed ones.More typically they are verifiably-bad sectors that will be remapped, at this point they will also be counted in 0x05. There are relatively few reasons for purely-transient errors, though they do happen, and do not indicate failure Some read errors may turn out to be transient, so are removed from this count. It could be a mistake when this data was written, it could be that this sector can no longer hold data - we'll know that when we next write to it. 197 (0xC5), Current Pending Sector Count: Counts sectors that showed a read errorīasically 'I couldn't read this, even though I tried pretty hard.because the disk itself reports this, which allows for some risky/misleading optimism (where pessimism is the correct response, as it gives you early warning that lets you saves your data) note that FAILED is a lot more informative than PASSED.SMART overall-health self-assessment test result: FAILED (or comparable if not using smartctl).Not to be confused with 187 / 0xBB, Reported Uncorrect If you want to notice these earlier rather than later, you want to occasionally trigger a SMART offline scan (not unlike a RAID scrub). Note that you may not notice present UNCs until you read every sector. When this also means the reallocated sector count is rising, the the drive is physically failing. Offline Uncorrectable:Īpparently counts the amount of UNCs as they happen. 198 (0xC6), Uncorrectable Sector Count, a.k.a.

(drives may have a few when sold, though those typically don't count towards this) Reallocations only happen when a drive writes to a pending sector, and fails to do so, which means the number of pending sectors is also important to check (see 197 / 0xC5 below). The best indicators of bad health are probably:Īmount of sectors that remapped by the HDD's firmware because it decided the original sectors are not viable anymoreĪ slowly increasing figure (of any magnitude) likely means a failing surface A largeish figure (hundreds to thousands) likely means the same.Ī few, or even a few hundred, might be fine, if constant over a long time. still, some of these values are better than nothing. There signs that sometimes strongly indicate that a careful person should replace the disk now - yet large studies have found no consistent predictor. SMART is less useful than it pretends to be.

mdadm notes, aacraid notes, OMSA notes, LSI notes.

Failure, error, and how to deal (concepts).

Current pending sector count