The error-correcting codes used by HDDs/SSDs correct or detect the most frequent errors, but sometimes, when there are too many erroneous bits in a sector, they can mis-correct the data and then the HDD/SSD returns a corrupted sector without signaling any error.

I have seen this a few times on HDDs that had been used for the cold storage of archival data, for several years (around 5 years or even more). For each archive file, I had my own hash values that were used to detect corrupted files, which allowed me to detect all such cases. I had duplicates for all such HDDs. Sometimes both HDD copies had a few silent corrupted sectors, but they were not in the same locations, so in all cases I could recover the corrupted files from their duplicates. If I had stored the archival data without redundancy, I would have lost it.

If you do not use hashes or other error-detecting codes for all your files, like I do, you may have had some failures in your HDDs without recognizing them, but such errors are much more likely to happen in files that have been stored for many years.

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ramses0 2 days ago | parent [-]

And/Or: `*.par` files.

https://en.wikipedia.org/wiki/Parchive

	▲	adrian_b 2 hours ago \| parent \| next [-]
		Yes, already for many years, I have also used par2create/par2verify for adding redundancy to archive files and repairing any corrupted files. However, I use both par2create and duplicate storage media, because duplicates that are preferably stored in different geographic locations are the only solution that guards against incidents so serious that they would destroy partially or totally the storage device. By itself, when an adequate amount of added redundancy is chosen, par2create is sufficient to recover archive files that are only affected by a few sporadic corrupted sectors, like on a HDD that has been stored in good conditions for some years. It will not help if the entire HDD becomes unusable, due to some mechanical or electrical defect, which may happen in HDDs used for cold storage, instead of being used continuously.
	▲	wongarsu 4 hours ago \| parent \| prev [-]
		Or rar files with recovery records. Same concept, but in one self-contained file instead of a number of sidecar files