Can't find a likely looking existing question so here goes:
I just updated to Yosemite and successfully (?? well -- it seems to work ) migrated my iPhoto library to Photos. Now however, I would like to move the iPhoto library to another external drive.
It is already on an external but I got a new one that I want dedicated to photos only).
So I thought I should quit Photos and copy the library to the brand new pristine drive. It looks like it's doing a major copy with a progress bar and all, and clanks and grinds for a long time then about halfway through it keels on an error,
The Finder can't complete the operation because some data in “Photos Library” can't be read or written (Error code -36)
and I wind up with nothing on the new disk.
So my question really what is wrong with the Photos library to begin with and how do I fix it?