Jeffrey J. Kosowsky wrote:
>  > 
>  > Backing up other backuppc servers is really a special case that might 
>  > deserve a special optimization.   But, I'm not sure that adding a 
>  > database automatically makes it any easier - unless you are thinking of 
>  > a common database that could arbitrate a common hashed filename that is 
>  > unique across all instances for every piece of content.  That's an 
>  > interesting idea but seems kind of fragile.
>  > 
> 
> Once we are talking about redoing things, I would prefer to use a
> full md5sum hash for the name of the pool file. You end up
> calculating this anyway for free when you use the rsync method
> (although with protocol <=28, you get a full file md4sum but with
> protocol >=30, I believe you have the true md5sum). This would
> simplify the ambiguity of having multiple indexed chain entries with
> the same partial md5sum.
> 
> With this approach then you would automatically have "a common hashed
> filename that is ['statistically'] unique across all instances for
> every piece of content."

Somehow the number of possible different file contents and the number 
possible md5sums don't seem quite statistically equivalent to me.  And 
then there's:

http://www.mscs.dal.ca/~selinger/md5collision/

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com



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