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I've been having a re-occurring problem reading data from self-burnt data Blu-ray discs. I'll try to copy the contents of a disc to an external HD and nearly every time, at some point during the copy, I'll get a -36 Error code from the Finder (data can't be read or written).

Just before this error the drive spins down and I can hear the head jumping around, like it's having trouble finding data. The drive will do that for between 2-10+ minutes before giving up finally and showing me the error code.

This tends to happen on similar types of file – usually files that are packages (Logic files, Photos library), Logic project backups and EXS24 sample files (AIFs). Sometimes copying that file again works, sometimes not.

These discs were originally burnt through the Finder and they all passed post-burn verification. So the question is: where might the problem be? Is it the OS? Is it the drive? Is it the discs? Really I have no answer.

(I'm running fully updated Mac OS 10.10.5, Blu-ray drive is a Samsung SE-506, discs are TDK-branded light blue face.)

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So I came up with a sort-of answer here. In short, a full copy of the Blu-ray was possible using the ditto command line tool:

ditto [source path] [destination path]

During the operation ditto does show errors (in my case Unknown error: 10000), but it does continue with copying the remaining files.

More detail

In figuring this out I started by inspecting the Console for errors during a Finder drag and drop copy. Sure enough an error was logged:

30/10/2015 19:54:57.000 kernel[0]: udf error: errno_t UDFFileNode::ReadPathComponent(uint8_t *, off_t *, bool *): Incomplete path component

On searching for 'mac udf error readpathcomponent error' I found this post on Adobe's forum which pointed to symbolic links being the problem.

Two types of file causing me an error were iPhoto and Photos Library files, and sure enough, within their packages there are symbolic links to certain .db and .apdb files. It appears the Finder attempts to resolve those links when drag and drop copying, but when it can't find that data (which isn't on the Blu-ray) it stops the copy and throws a -36 error.

To confirm this I looked for another way to copy the files, finding the ditto tool. Supporting my theory, the errors ditto threw up during the copy all related to symbolic links. So this might be a Finder bug rather than a hardware problem.

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