Can't copy files from one hard drive to another (same sizes) I have two external hard drives, both 2TB. I've been using one as a time machine drive and have filled up about half of it. The other drive isn't being used as a time machine, but rather I got it to save larger files; I've taken up very little space on it so far (only a few megabytes).

I want to give the time machine drive to my dad so I'm trying to copy all of it's files into the other drive. When I drag the Backups folder from the TM drive onto the destination drive, it partially copies everything over and then says the drive is full. Sure enough, I checked and it has somehow filled up all 2TB despite the source drive only having about 1TB of data. 

Does anyone know why this is happening? Neither drive is encrypted and they are both using a Journaled file system.
Time machine uses Unix hard links. This is confusing the copy software which results in the same file having multiple copies. 

Here is how to make the copy according to Apple.

https://support.apple.com/en-us/HT202380

So, give your father the other drive.  I read somewhere where it's not best to mix in non-time machine files on a time machine partition. Seems reasonable to me.