This one I caught a few hours ago: happened while archiving some Nintendo 64 ROMs.

Miraculously, the initial transfer from two days ago did not corrupt any of them (those are big endian; also lucky, because there is no local mirror...), but copying them for the byte-swapped conversion set directly on the server corrupted one ROM in that copied set. This is becoming much less frequent, at least.

Checked RAID5 status, array is fine. This issue shows up over a wireless network; should try wired network and local transfer... and probably examine the SATA ports on the motherboard, among other things (which I may eventually replace anyway).