For the context you have provided, I think, you could say this: - If I had (or If there had been ) enough space on my HDD [but I didn't have / there wasn't enough space on it], all the files would have been downloaded by this morning [but all the files didn't download by this morning]. Also, you don't really need 'already' there, because 'by this morning' has the meaning 'before or at the point the morning came to an end.
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