bug#69535: update

[brian]

Sorry for the delay in updating this problem - I've been doing some 
testing!

The first thing I did was wrote a quick and dirty Pascal program to do 
a byte-by-byte comparison of the data files, just in case it was cmp 
that was causing the problem, not cp. The results were the same using 
my program. OK, so cmp is innocent.

I then wrote a program which generated 40 GB of more or less random 
data - 200,000,000 fixed length records of 200 bytes each - and sent 
it to a friend with the request that he do the test I did, i.e. 
generate the file, copy it, and compare the copies. He's also using 
Mint 21.3, as I am, but with a different type of drive. The files 
compared correctly on his system.

OK, so the next thing was I tried using different drives. I have a 2 
GB SSD in this system, so I tried that. No problem, the files compared 
correctly. I got the same result using my RAID 5 backup device, which 
contains 5 of the same type of drive as was producing the error when 
connected direct to the SATA port, but obviously the backup device's 
software has an effect there.

So, the bottom line is that I'm chasing some kind of goofy bug which 
likely involves the drivers for my hardware - a 14 TB Seagate 
connected to the mobo SATA port - and cp is also innocent.

Please consider this bug report to be closed. I'm not sure if/how I 
can do that via e-mail.