Move file from HDD to SSD
If the source and the destination of the file is on two different volumes, OS X's default is to copy the file rather than move it. In reality, what you want to do to the file is to copy it to the new location and then delete it from the old, whereas if you move a file to the same volume it's originally on, it will just change the recorded location of the file.

You can achieve "move" (copy-and-delete) functionality in Finder by holding Command when you drag the file.