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Chronosync - Byte by Byte Comparison

Discussion in 'Workflow Discussion' started by Russ Ford, Dec 1, 2016.

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  1. Russ Ford

    Russ Ford New Member

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    Hi,

    Is it possible to undertake byte-by-byte comparisons within Chronosync? I understand Chronosync can be set up to undertake verification after copying, but can it do full verification as part the initial comparison?

    I also use Deltawalker which does allow such comparisons, but I prefer the way Chronosync allows you to save container documents, etc.

    I have checked the user manual but can't find any reference.

    Thanks in advance.
     
  2. Jack Henry

    Jack Henry Active Member

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    What are you refering to when you say 'initial comparison'?
     
  3. Russ Ford

    Russ Ford New Member

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    With chrono, if I do a comparison of my photo folder with the back up, each containing 10,000 photos it takes about 30 seconds and presumably it is just checking the file names and all metadata. If it copies any files across and the verification box is ticked then it will do a verification check (byte by byte check?) of just those files it has copied.

    With Deltawalker it will do that same 30 second scan as above but if I select the Byte comparison box then it will do a detailed check of ALL photos and takes about an hour (in the settings it says it has to open each file to do this).

    Clearly it's not a check I need to run all the time but it is quite useful to do every so often and I would like to run the same test in Chrono since it is much easier to set up than Delta with the scheduling, etc. But I can't see how to do it.

    I can ask Chrono support team but I know it's a popular app with this community and wanted to make sure I am configuring correctly.

    Thanks
     
  4. Victoria Bampton

    Victoria Bampton Lightroom Queen / Owner Staff Member Administrator Moderator Lightroom Guru

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    Ask the developers Russ, because I'd like to know the answer to that too.
     
  5. LouieSherwin

    LouieSherwin Active Member

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    One of the issues to be aware of when evaluating copy verification techniques is the effect of the filesystem cache buffers in your system RAM. Basically the problem is when you copy a file from diskA to diskB and then read back the copy from diskB what you get is the copy of the file that is still in the filesystem cache not the one that was actually written to diskB.

    This issue was discussed by the author of Carbon Copy Cloner (CCC). His suggested solution is that you must run a completely separate verification pass on the entire disk partition. This will in effect flush the filesystem cache and force the operating system to read each file from the disk.

    I am also curious to see what ChronoSync has to say about this.
     
  6. Russ Ford

    Russ Ford New Member

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    I contacted Chronosync, this is their reply:

    QUOTE
    ChronoSync doesn't have a feature where you can run an operation that compares the contents of all items in the two chosen Targets. ChronoSync's data verification feature is performed after copying data and only applies to the items copied.

    We go to great pains to make sure ChronoSync is reading back the actual data rather than cached file system information, so you should feel secure in that when ChronoSync does perform data verification, it is looking at the actual data and not getting cache hits.
    UNQUOTE

    So, on reflection, I think I will use Chrono for incremental back-ups as the new data is verified but periodically will use Deltawalker to perform a complete byte-by-byte comparison of the original and back-up folders to ensure the back-up retains its integrity. This is probably a belt and braces approach as comparing the files in Chromo using the file length as a trigger is probably sufficient to highlight any problems.

    Would welcome suggestions from others as to what they consider the most effective back up approach to be.
    Thanks
     
  7. Jack Henry

    Jack Henry Active Member

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    If you've done an initial back up of a folder with ChronoSync, and that folder has been verified, then any further syncing and verification should be indicitive that the entire folder is correct. If the initial files have been verified and then subsequent files verified, you can be sure that all have been verified, albeit at different times.

    It's like counting 10 objects as a group of 10, or 2 groups of 5, or 5 groups of 2. No matter how you count them, you still can be sure there are 10 objects there.
     
    Last edited: Dec 6, 2016
  8. Russ Ford

    Russ Ford New Member

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    Thanks Jack. The assumption you are making is that the initial back-up was done with Chrono, and if so, then I agree that incremental changes will then be verified. Although as we all know hard drives are never completely reliable and so the option to undertake a full check periodically would be a useful one I think?

    I did have a follow up email from the Developer:

    Activating the File Size Trigger is a good safety measure. I know we have a feature request/enhancement logged to be able to verify all previously synced items so maybe it will be included in a future release.

    I logged your support for this existing feature request in our system.

    So I guess its a case of watch this space!
     

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