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Just finished a copy of an external drive (exFAT) to another drive (HFS) using standard the Finder's Cmd+C, as I want to format the first drive (exFAT) to HFS. Now, I've been trying to verify all the copied files using -diff and -rsync for several hours, but for some reason, Finder has printed a "._" on all of the files on the exFAT drive, but excluded that on the destination drive. So naturally, both commands will tell me that all files differ, when they're actually the same in every other aspect.

So, is there a way, maybe a certain flag or something, that lets me use either the diff command or dry rsync command to display any differences apart from that "._" added to the file names. For instance, I used md5 on two files, and their checksum's identical, even though their names differ.

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You're misunderstanding what the dot underscore files are.

They are resource forks or extended attributes that ExFAT drives cannot hold, so the Mac separates these out into invisible files that ExFAT can hold. These files will be tiny. ExFAT also cannot hold regular unix permissions - these will often be lost.

If you copy them back to a Mac-formatted drive these are automatically 'folded' back into the main file, so will appear to 'vanish'.

You need to be most careful when using ExFAT that you don't copy Mac bundles, such as Photos libraries, Logic Pro files etc, as these can be badly damaged in the transition. ExFAT will treat them as folders & they may not get correctly re-assembled later.

I'm uncertain as to whether this will render any attempt to diff the files useless, or whether diff will ignore the attributes & only consider the contents. Either way, you can ignore any dot underscore files.

In short - don't use ExFAT for Mac files unless you must use it for cross-platform compatibility. If you need to do this a lot, I'd consider getting an HFS-capable win/nix utility & stick to HFS+.

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  • Well I'm in the situation where i absolutely do have to copy files safely from an exFAT drive to an HFS drive. And yes, the files included are logic files and they are the most important ones, I would say. And I need to know that they were copied correctly. Should I perhaps use some kind of utility for this?
    – Timeweaver
    Oct 18, 2022 at 12:41
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    Then just use Finder, drag & drop or copy/paste. If there's an error it will tell you. If not, then nothing to worry about. Anything that got truly broken on its way to ExFAT won't be fixed by the copy back, so it would appear to be the same anyway.
    – Tetsujin
    Oct 18, 2022 at 12:43
  • Ok, thank you for that! And you're positive that with zero error-reports, the files will be intact?
    – Timeweaver
    Oct 18, 2022 at 12:45
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    With zero errors the DATA is intact… but not necessarily the relationship between the raw data & the perception of the Mac with it as a Logic project. I'm in a big FaceBook [180k +] group for Logic Pro - a common issue is people who saved or transferred projects to ExFAT. I don't recall anyone coming up with a definitive fix yet, but really, don't use ExFAT for Logic files. It causes a lot of trouble. You're now in the position where you just have to see if they will open. The damage was done on the way to ExFAT, not on the way back.
    – Tetsujin
    Oct 18, 2022 at 12:47
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    I wish you luck. Remember to make it GUID/HFS+ rather than try perch it on MBR. You have to Erase the entire drive to do that, not just any partition.
    – Tetsujin
    Oct 18, 2022 at 12:53

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