Verify Media MD5 Error - But file is identical to backup?

[jhg]

This is parallel to my other question about Verify Media MD5 errors

 

I have an HD archive set that gets two MD5 errors when I run Verify Media. However, if I restore the two files in question (to a different location) and then compare them to the originals, they are identical. 

 

What would cause Retrospect to report an MD5 error when the files are in fact identical (as confirmed by various methods including WinMerge and Cygwin "cmp" command).

 

The two files were originally archived to the HD in 2012 and 2014.  Have there been any changes to the MD5 algorithm used by Retrospect that could account for this?

[Scillonian]

Have you run the verify media more than once? Is it always the same two files? How is the HD connected to the server?

 

Only one bit needs to have changed to change the MD5 value. If you haven't done so already verify the media again and see if the same two files fail again to eliminate the chance they were just random failures.

[sowen222]

I've had this happen as well over the years, usually with JPG files. Once you get such an MD5 error, it always reports it with the same file, even if you back it up again (unless you change the file in the meantime, of course).

 

On two different occasions, Retrospect backed up two different JPG files, reported an MD5 error during the verify so Retrospect assumed they were not backed-up properly and kept trying again the next time, with the same MD5 error as a result. In the end, my work-around both times was to open the file and save it again (thereby changing the content).

 

Retrospect's MD5 algorithm apparently has a problem with particular binary streams. Either that, or hard-drives are sometimes unable to record a particular binary pattern - odd, but I've heard of it happening.