Well, maybe the error correction on hardware or firmware levels has its limits, since I have seen files with bit rot. I still keep one such file, a few GB in size, in which some bits evidently are wrong. All files were saved on HDs and then read, years later. Unfortunately, I didn’t even think about creating md5 sums of them immediately after acquisition.
While the change of file’s content can take place because of various reasons, in two cases I suspected a defect which was magnetic in nature, and investigated. I checked the HDs in a variety of ways, from soft non-data-destructive tools to using the tools from manufacturer. All tests showed healthy HDs. How does one explain bit rot then? Data from HDs was backed up regularly, but the content was not visually checked. I discarded the HDs.
Another interesting statement from the article:
“It’s a common misconception to think that RAID protects data from corruption since it introduces redundancy. The reality is exactly the opposite: traditional RAID increases the likelihood of data corruption since it introduces more physical devices with more things to go wrong.” There is more explanation in the article, reasoning that non-catastrophic failure of a disk in RAID leads to data corruption.
I don’t use RAID and advise colleagues not to use RAID for storage, and only to use RAID0 for speed. “For storage, use single disks and make backups instead of relying on RAID’s abilities,” I say to them. I have read somewhere that Google does not use RAIDs for data storage, but this information may be old or wrong.