https://en.wikipedia.org/wiki/S.M.A.R.T.https://en.wikipedia.org/wiki/Data_degradation
As I said earlier
I see it a few times a year, people who think their backup is good because it verifies but when it comes to recovering it, not so much.
Why would this happen? Is the verify no good? I believe Teracopy does a bit wise test, it takes just as long to test as it does to copy the files. The files are not encrypted, they are the same as the original.
A simple example
1. from drive 1, read file in to memory1
2. From memory1 write file to drive 2.
3. From drive 2, read file in to memory2
4. Compare memory1 to memory2 for match
This is fine until
1a. Memory1 changes and computer does not use ECC memory Or Memory1 is bad.
2 writes bad file, 3 reads bad file and 4 verifies bad file matches bad file.
a change to
1. from drive 1, read file in to memory1
2. From memory1 write file to drive 2.
3. From drive 2, read file in to memory2
3a. from drive 1, read file in to memory3
4. Compare memory3 to memory2 for match
This change would have catch to catch this.
Some here will say small chance( true) but memory errors do happen.
You are still assuming that to/from disk surface to/from memory is perfect.
The above links describe other errors that happen.
What I am reading is making many copies of a file with unknown status and no easy way for computer to know if file is good or bad.
https://en.wikipedia.org/wiki/ChecksumA file checksum is one way that can help.
It also sounds like you want an archive more then a backup and be able to create many copies of the archive.