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If I backup a number of directories, then move a file between directories, a full backup will normally copy that file again, even if it hasn't changed.

I believe a normal incremental backup will also recopy the file. But I also think some backup systems manage to avoid doing so, by keeping track of already-copied files.

Is there a standard term for this problem or for the software feature which mitigates it?

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up vote 2 down vote accepted

the term should be 'deduplication'

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Look for a backup solution that keeps each unique file only once no matter how many time's it appears on the system. This is usually done by generating hashes (MD5 commonly) and indexing/storing the files based on this data. – Chris Nava Nov 17 '10 at 20:05
@Chris Nava: what you describe is called 'deduplication' :) – akira Nov 17 '10 at 21:19

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