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I have a folder on Drive 1 called Music, and it is 100GB. I have a folder on Drive 2 called Music, and it is 116GB. It's the most updated version. How do I copy the Music folder from Drive 2 to Drive 1 without having to rewrite every single file?

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Which version of OS X are you using? –  Nix May 13 '12 at 21:59
I am using 10.7.4. When I copy the folder from one drive to the other, I'm asked if I want to replace. No merge option. –  dallen May 13 '12 at 22:02

3 Answers 3

up vote 2 down vote accepted

The merge option will only show up if you are copying (rather than moving) the folder. Make sure you hold option while you drag the new folder to the location of the old folder. Alternatively, using +c to copy the new folder and +v to paste over the old folder should give you the option to merge the files.

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This is a classic use case for rsync:

rsync -av /source-path/source-dir /destination-path

rsync will copy only new and changed files to the new location.

It is important to understand how a trailing slash on the source argument functions. If there is a trailing slash then the contents of /source-path/source-dir will be copied to destination-path. If there is no trailing slash then source-dir itself will be copied to the destination and its contents will be another level down in the destination hierarchy.

So if you want to replicate one path to another include the trailing slash as follows:

rsync -av /sourcepath/sourcedir/ /duplicatpath/sourcedir/
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Not sure why the default Lion Merge button doesn't show up for me. But I ended up using ditto. Found here: http://superuser.com/a/221599/102789

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