First these counters vary in meaning and support by vendor/model, and it would be nice if someone were to come along and mandate further standardized ones. Inst

First these counters vary in meaning and support by vendor/model, and it would be nice if someone were to come along and mandate further standardized ones. Instead you have to tune everything for each drive model. In this regard SCSI is a little better (more on that later). Second, timeouts and uncorrectable errors are generally being reported to the controller as part of normal operation. So having SMART tracking them is just a bonus. Either of those two conditions is usually sufficient to kick a drive out of a functional RAID array because those are data loss events. Most drives have layers and layers of ECC, so in order to get an uncorrectable error a lot of bits need to be flipped in the target sector. For that to happen it likely indicates there is something mechanical going on which is likely to affect adjacent tracks/sectors. Of course if you never scrub your drives its possible bitrot accumulates on a perfectly functional device until sectors aren't recoverable. In my previous life I found it much more interesting to track the rate of soft error counts during scrub operations. Particularly, in larger arrays because sometimes a drive would start getting slower (which is frequently caused by read retries in the drive itself or problems tracking the embedded servo/etc) and the correctable error counts would start to steadily rise followed by actual timeouts/uncorrectable errors. Of course these days, it seems most drives won't show the correctable error counts because it would freak people out. Instead you have to infer it from seek errors and relocated sector counts. Although, it might now be considered a SAS/SATA differentiator. SCSI has standardized log pages with more detailed information. (random google hit http://www.seagate.com/staticfiles/support/disc/manuals/scsi/100293068a.pdf http://www.seagate.com/staticfiles/support/disc/manuals/scsi... page 238) Note the errors are categorized as corrected without delay, with substantial delay, and corrected on a retry. By comparison the SMART data isn't particularly "smart".