There’s a few ways. First is this for backup purposes only or are you going to use the new hard drive? If using the new hard drive:
One is to simply drag and drop it all to the new hard drive (or use a utility like Hedge or Shotput or any other file copy utility). Then open the new library on the new drive and relink to the media on the new drive.
The other way is to use FCPX and you can copy the media using the file menu and media management capabilities in FCPX. The downside to this is that FCPX will rearrange the media and it won’t stay in the structure that is in the Finder.
If for backup, use a utility like Chronosync to sync everything from the one drive to the other and you can set it up to run syncs periodically to keep it all aligned.