Yeah check that the hard drive(s) are ok. However, I used to have similar problems a couple of years ago, to me it seemed it was related to USB3.0 in Windows 7 because back then I had other USB3.0 problems as well, like the external drives suddenly getting disconnected if I was copying lots of data to them etc. Apparently the Windows 7 USB 3.0 drivers were crap or something, but nowadays, at least after reinstalling Windows 7, I don't recall seeing these problems anymore.
This didn't happen if I used USB 2.0 (e.g. my USB 2.0 hub), and for some reason I had these problems only with external USB drives, not e.g. USB flash drives.
A couple things I have used and use to make sure copying and moving files goes ok:
1. Earlier I used
Teracopy for copying or moving files, especially when doing it to those external hard drives. It has an option that it automatically double-checks after file copy or move that the target files are ok, that they have the same CRC32 checksums as the original files. If it detects problems, it will perform the file operation (and verification) again.
I haven't used it lately though, I had some issues that when I had two (or more) accounts in Windows 7 and installed Teracopy on one of them, it didn't seem to work fully on the other accounts. It worked only on the account where it was installed even though it was visible also on the other accounts. Maybe the program's support for multiple Windows accounts/users was incomplete or something, but if you are using just one account in Windows, I guess this doesn't matter. Also I don't know if this works in e.g. Windows 10, the page mentions support only for Windows 8 (I used it in Windows 7).
2. Nowadays I mostly use
DVDSig if I have e.g. several files I want to copy or move to the external hard drive. I put all the files to be copied in one folder, run dvdsig "scan" in it (this creates a md5 checksum for all the files in the folder), copy the whole directory to the external hard drive, and then run dvdsig "verify".
If I want to scan and verify my whole external hard drive (2TB or 3TB), I use
RHash instead of DVDSig. DVDSig is easier to use for quick checkups, but rhash is more heavy-duty with more options, and with e.g. these benefits:
- It has support for even more advanced checksum algorithms than mere CRC32 or MD5.
- DVDSig didn't seem to be able to scan and verify files which were either very very small, or had some non-ASCII characters in the filename. RHash has no issue with those. For GOG installers and extras files this is not an issue though, they are not too small nor have odd filenames.
- RHash has an option to add checksums for new files it detects, so that you don't have to re-create checksums for all your files every time you add new files to e.g. your external hard drive. That would be silly anyway because if some of the old files have become corrupted in the meantime for some reason, then you'd create new checksums for the corrupted versions.
- RHash is multiplatform so you can use it for your files in Windows, Linux and whatever. DVDSig and TeraCopy are Windows-only I think.
In the long run, I hope filesystems like
BtrFS become more commonplace, as they have file integrity check built-in to the filesystem itself so you don't have to use extra utilities like these. They will notice (and even try to fix) if some file gets corrupted during some file operation.
