I'm currently trialing the free month with Google Play Music (GPM) and am thinking about uploading my music library.

My question is ... if my music library is 80GB, will I use 80GB of data to upload to GPM?

Or does GPM simply read the ID tags in my library and link to the relevant version Google's own library - in which case very little data would be used in the process.

If the latter, what if I have songs that Google doesn't?

I've tried to find on the web a clear explanation of how the upload process works - but have failed. So any links that address my questions above would be appreciated.

cheers