rsync checksums

Karl Kashofer karl.kashofer at
Sun Apr 27 21:06:00 GMT 2008

Hi all !

I am currently trying to find a smart way to long-term-backup my data.
I currently do link-dest-updates to an external hdd. However, I am concerned 
about data corruption in the backup or the original, i.e. corruption of the 
data inside the files.

Thus i am wondering if there is a way to check the integrity of the backups on 
the external disk. i.e. to avoid data degradation for example when the hdd 
starts dying.

What i think are two things:
rsync calculates a md4 checksum of every file transferred. 
Would it be possible to store this checksum for future use, i.e. to recheck 
the files of each rsync snapshot at any later time ?

If not, could you suggest a tool to do that, keeping in mind that most files 
will be hard-links which I dont want to check in each backup (i.e. 
find+md5sum wont work).

And a question about the --checksum option:
What happens if --checksum finds CRC differences in a file which has the same 
size and modification time as the copy in the archive ? 
Would that not be a highly unusual thing to happen, showing some kind of data 
error ? Could this be used to alert the user about possible data corruption 
in the original or the backup ?

Thanks for your time,
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