I may be off on a wild goose chase.
I was thinking that because the data on an SSD is so scattered/fragmented as compared to that on an HDD, the SSD's directory (that we erase in a simple erase procedure) for a volume must contain much more information than the directory for the same volume cloned to an HDD.
Guess not?
To the best of my knowledge, no current FS changes file or directory layout in response to media type being SSD. It would make some sense though, since fragmentation isn't a problem.
Example: when you are appending to say, a text document of a book you are writing. Every so often it either auto saves or you save manually, increasing the file's size. Since the computer's been busy doing other things, it's already written stuff off to the hard drive right after the end of the file. So it has to allocate blocks somewhere else, away from the rest of the document. After doing this several times, (mac os says 8 fragments iirc) the OS says "ok we need to pick this up" and the next save will be entirely moved to a different spot on the hdd where the entire file fits in one continuous chunk. This prevents multiple head seeks to read the file.
An SSD would not require this at any time.
The same problem can apply with a directory, which is also stored as something like a file. Adding files to a directory requires the directory to expand its size, and possibly occupy non-contiguous clusters. After a certain point, the OS will usually "gather and move" it, to defragment it. I don't know if OS X still tries to do this sort of thing on SSDs or not. But if it did, it would be a waste of time.
So the result is that if it doesn't do it, it doesn't help. If it DOES do it, it still doesn't help. So there's nothing to be fixed when copying FROM ssd TO hdd. Going in the other direction however, would benefit the hdd to be defragged. But that's done as a part of the copy process anyway since the copy is linear from one file/folder to another, not random, which is what causes fragmentation. So there's nothing additional that anyone needs to do, it's already doing what it should.
