SSD case: Bad sectors on SSD
The health and generic usability of the SSD decreases, bad sectors reported
While most solid state disks (SSDs) report lower health only related by the wearout caused by writes, in many cases we can find bad sectors on SSDs too. The symptoms are usually:
file(s) and/or folder(s) may be not readable or damaged/corrupted.
the SSD may be much slower than expected, usually read speed is very low for some data (if the file(s) could be read at all).
the complete system may be slower than expected or may not able to boot the system as the SSD may not be (always) recognised by the system.
bad sectors reported in the text description: There are 16 bad sectors on the disk surface and/or The drive found 1 bad sector during its self test.
the S.M.A.R.T. page may show increased value at attributes #5 Reallocated sector count, #198 Off-Line Uncorrectable Sector Count or similar attributes.
Bad sectors on SSDs
Yes, even if many users think the opposite, SSDs can also have bad sectors. Even if SSDs (generally flash storage) does not contain mechanical parts, the sectors (memory cells in this case) can also fail - and with time and usage (and wearout), they usually FAIL. The question is WHEN they fail and how much amount of data may be lost/damaged then...
SSD bad sector diagnostics
Exactly as with hard disks, usually SSDs with bad sectors show failure during internal self test functions (Disk menu -> Short self test, Extended self test):
Similarly to hard disk drives, the bad sectors on SSDs are also already reallocated (so they are no longer used, as the SSD reads/writes the spare area instead of the original bad sector) so they should not cause more problems. Manufacturers even allow more or less bad sectors: manufacturer-specific tools may not display any problems or can show "perfect" status even with some bad sectors (until a defined error-level threshold reached). However the Disk menu -> Surface test -> Read test can still show unreadable sectors and if the Detect file information for sectors with errors option enabled, Hard Disk Sentinel automatically detects and shows the affected files (see the bottom).
Recommendations
In this case, the Disk menu -> Surface test -> Disk Repair function can help to improve usability (just like for weak sectors found on hard disks) but usually the SSD may not be reliable: we may expect more and more problems with time. This is especially true if the health level is low, due to high number of bad sectors already found and/or caused by wearout of the SSD.
If we experience similar again and again, the Disk menu -> Surface test -> Reinitialise Disk Surface test is useful. It deletes all files, folders, partitions, master boot record so should be used after complete backup only, when the SSD connected as a secondary drive (not used as standalone system drive). The Reinitialise Disk Surface function can greatly improve the status of the SSD by forcing reallocation possible further bad sectors (if required, just like for hard disks) and re-write all memory cells. As a result, the SSD (or any affected flash storage, like SD card, pendrive) may re-gain performance and (as problematic sectors stabilized) can be still used for longer time - with constant monitoring and backup upon any new problem(s) reported.
Bad sectors on flash storage
Bad sectors can happen on solid state drives: SSDs with SATA/SAS/NVMe/M.2 connection, flash drives, memory cards too in addition to hard disks. We may think bad sectors can only happen after excessive amount of writes and we'd need to focus only on the Lifetime Writes displayed on the Overview page and how it's related to the Terabytes Written (TBW). But it is not true: bad sectors can happen even with very light usage. In this example, we encountered bad sectors on an SSD with not too intensive (office) use. Fortunately, the early detection and the relatively high health allowed the complete backup, just some recent Windows update files damaged.
Without the SSD health monitoring and early warning, many additional files and the complete partition could be damaged / corrupted / lost.
Monitoring the status of all SSDs with accurate, error-sensitive method is very important to know possible degradations, new problems. These can be related to both bad sectors and generic wearout caused by write commands: both can cause SSDs to fail - or "just" data corruption, data loss (or degraded performance in best case). Hard Disk Sentinel can help greatly to monitor and report possible problems not only for hard disk but also for SSDs by all kind of connections and the early-warning system allows us to prepare: to perform backup and diagnose/fix issues or replace if required.
Manufacturer-specific tools may not report problems as we expect. The purpose of those tools is only to reduce warranty (RMA) requests, so usually they may show SSDs as "perfect" even if it may have lots of bad sectors and/or other problems (but this may be true for hard disks and related tools which may be not sensitive / informative enough to detect and report all problems and degradations).