But there's two factors to consider...
A) A physical issue with the disk. In this case, SMART shows an error and increments the value showing a portion of the disk is unusable. This happens only when data is read and can't; or data is attempting to be written and can't...
Excuse my necromancy, but, even data which looks bad (unable to read/write & SMART errors) tend to have many options. While there are some issues which are big problems (Service Area, Drop Damage, R/W heads, etc) ... here's a little flowchart of diagnostics & solutions.
Serious // Global errors are often in the Service Area (or 'SA' ... which is BIOS info,
logic or initialization code) Firmware written to the platters for the manufacture's convenience; the outer-most-tracks on most HDs (usually 0, 1 with backups on others). This is where data like the G-List (Grown list: errors accumulate after mfr.) + P-List (Permanent List: Defects in the substrate at the time of mfr) will be written. All drives must successfully read the SA to allow the armature to begin 'flying' ... usually, SA issues
don't preclude operation (but can) as most modules aren't critical and those which are will often be available
in duplicate. But, there are special manufactures or series that truly suck ... such as WD passports (garbage -- no SATA interface & are encrypted no matter what!) ... & Seagates ... who's consumer drives are crap.
HD issues you WANT ... appear due to the ATA commands which report blocks that
reads slowly in
binary "pass fail" terms. Which may in fact, only be a block that reads slowly ... it could mean that the PARITY for that block wouldn't be read, (can also be firmware issue). It could have been erroneously added to the G-List (the error table in the HD Service Area). While I'm unsure what FreeBSD's time out rule is, the Windows
definition seems to be the average for OSs (perhaps the POSIX driver) which is predicated on blocks which exceed 600ms.
HFS+ & APFS may be the same as NTFS time out... Despite how annoying it is macOS doesn't natively speak NTFS, & no matter how counterintuitive, Steve Jobs wrote the HPFS (high performance FS) which is NTFS...so, it wouldn't be surprising if the rules were recycled. But, they are just that; rules.
Unlike the laws of physics for which there are no penalties for transgressing, as they're merely arranged such that violations are impossible. Fortunately, our rules can be altered -- and are. I've heard free tools may allow you to modify the time out duration (maybe DD Rescue) definitely
HDDSuperTool does, but I'm more familiar with professional tools such as DDI 4 (DeepSpar Disk Imager 4) which allows you to manually control the time out speed of every block read. You'd read the first-pass with fast time outs to avoid taxing the drive in one zone prior to reading the... 97% ..? which may be accessible. With a DDI4, you just grab tougher data in successive passes. Set the time outs to 6s if you want -- & combine that with other
I.T.T.T. rules (aka,
If This Then That). Eg, if the previous 10 blocks failed to read with 1000ms time outs, skip 100 or 1,000 blocks and try again. Maximizing the data read without risking global failure. Importantly, we can also instruct it to IGNORE PARITY in a later pass. In those blocks parity can't be read for whatever reason, we can read those blocks _
x_ times ... to average the result. Weirdly, my more expensive tool (PC-3000 Express which costs ~5x a DDI or ~$17,000) ... doesn't have that feature, but none the less is more capable. Perhaps, performing some of these tasks more autonomously.
Obviously, some issues involve a weak or failed transducer // R/W heads ... or the preamp heads are connected to -- also on the armature. HDD data isn't always digital; were you to hear what the R/W head sends, you'd hear a waveform where high pitch = 1 & the low pitch = 0. These [are]
discrete values vs. the resolution of the frequency, able to be every value between that range (aka
analogue)... it's
discrete during transmission, once the digital state's read via the transducer. If a single head is bad, we can disable it, too, & recover the remaining heads.
Hope this was useful for someone ...