Re: evaluating backup systems: rsync

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On 01/19/2013 01:21 PM, John Hinton wrote:
> On 1/19/2013 1:28 PM, Nicolas Thierry-Mieg wrote:
>> See man rsync:
>> Rsync  finds  files that need to be transferred using a “quick check”
>> algorithm (by default) that looks for files that have changed in size or
>> in last-modified time.
>>
>> and yes I've tested this before posting  ;-)
>>
>> to avoid this you need to use --size-only .
>>
> Yet size only is not reliable. If for instance you have a simple text
> file with the word hellO and someone catches the typo and changes it to
> hello, the filesize doesn't change as near as I can see. Both show as 6
> using ls -al. Unless rsync uses a more granular check of filesize that I
> am not aware of? If this is the case, then someone could potentially
> edit a large document fixing numerous simple typos and wind up with the
> same filesize.

And then there is prelink, which changes the contents of files without
changing either the size** or the modification time. It's the topic of some
very messy code and nasty comments in my backup scripts.

** The very first time a file is prelinked, the size will change. Subsequent
    prelink runs may change the content, but will not affect the size.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.

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