Windows 7 - Files corrupted after being copied to a different hard drive

I copied several large files (between 1 and 4 GB) from one USB hard drive to another. At the target destination several of the files had defects. They were in general not completely unreadable. Most could still could be opened but had clearly corrupted data.

My question now is how does this happen and how can this be detected/prevented.
Doesn’t Windows 7 have some kind of an integrity check when copying files?

Also is there any good software to compare files for being exactly identical down to the last bit? Ideally with the capability to compare whole folder contents so that it hasn't to be done file by file.

Thanks

I had a similar issue awhile back. To make a long story short it turned out to be a bad ram module. Similar to your issue the data, whether copying between drives or downloading from the net, (depending on the size), would be corrupt. The fact that it was only with a certain size or larger file gave me the clue.

Tested this by switching the ram out, leaving only one stick in at a time. Took a little while but was able to track down the bad ram and confirm. Anyways, changed the suspect ram out and all was good again....

I ran the full memory test of the Dell System Diagnostics (Dell Drivers and Utilities Disc) which found no problems. So it doesn't look like it is the same issue you had.

You had copied the file not cut and pasted it. In that case delete the corrupt file and try to copy again.

Yes, I copied the files. After detecting the damage I recopied the corrupted files and then they were OK.
But it is quite tedious to go through each file and look for little defects or data that are off.
So the real issue is to detect if a file was copied correctly or if it was damaged.
What I need is a program to compare the copied file with the original on a bit by bit level. Ideally a program that can compare entire folder contents.

Please go and read this A Brilliant File Verification tool: A Second Opinion For Your Data web-page. May be you shall find the information useful in sorting out your problem. But there is just a possibility that the cure may be worse than the problem.

I've been using FolderMatch for quite some time to do such things. You don't have to synchronize a whole folder, you can just use it for individual items. When it gets through, it compares the files, so you know right then and there whether there's a problem, and it does this automatically. The program is not free, however. The only problem I had with the program is that it had problems copying files with some foreign characters in the file name (it did not like Turkish characters, but did not seem to mind Spanish ones; I haven't tried any others).

The best way to deal with this problem is to solve it so it doesn't continue to happen. You shouldn't have to deal with manual verification of files when copying them from one medium to another. Something is obviously awry with your system or drive(s). I would be running Disk Check on both of the drives in question to see if there are any disk issues causing this.

I would also run an independent (of Dell's utilities) memory test.

Download the Memtest ISO from here:

Memtest86+ - Advanced Memory Diagnostic Tool

Burn it to a CD and boot your computer from the CD to run the memory tests to see how it's performing. Run it for at least 3 passes and see if there are any errors.

One wonders whether all the file corruption you mention was done on one occasion or several. I cannot help wondering if, at some point, you thought everything was done and turned off the affected hard drive in question while ignoring Windows telling you that it was still in use, or else forced a shutdown when Windows was taking forever waiting for "background programs" to close. Windows loves to tell you that the hard drive is in use even though you find no applications via task mgr using it. Do you always dismount the drives using the Windows gui? Have you ever accidentally powered off one of them, or even intentionally done so because you "thought" nothing was going on?

If your memory is okay, my SOP would be, first, to run a complete check disc on your pc: check the box that says "scan for and attempt recovery of bad sectors." That will take a while. Next, do so with the external drives, first with the one that had the bad files. That may take a day or longer if you are using usb 2, but don't skip it.

While check disc is scanning the one drive, do a complete anti-malware scan--including a scan of the other external drive, the one check disc is not checking--with your resident program, followed by a complete scan with Malwarebytes and Superantispyware. When check disc is through with the one drive, do the complete multi-scan for malware on it. Once everything is done, I would also defrag all the drives: if you have pieces of one file in 800 different places, that makes it difficult for Windows to keep up, and, with large files, it is much more likely that the files in question will be fragmented. Keep the external drives defragged.

You did not mention whether you can replicate the errors. Do errors only occur when copying to a certain hard drive?

I forgot to mention one other thing about what I consider to be SOP: run sfc after you run check disc, and then run KB947821. I run both of those religiously, but you do have to check every now and then to make sure there's not a new version of KB947821; the most recent version was published on 08/23/11.