Copy Mac Time Machine Backup Directories from One External Drive to Another

Solution 1:

Funnily enough, starting with macOS 10.12 the Finder has been granted special powers to perform an 'exact copy' on Time Machine archives. Use the Finder and only the Finder to give your .backups new homes, because Finder will maintain not only all permissions and metadata but either maintain or translate inode references for each item in the backup.

Solution 2:

You can't really. Time Machine uses hard links for directories and rsync (especially the one with macOS) does not support this.

However in this case the best way to get two Time Machine is to select two disks as Time Machine disks in Time Machine Preferences. To create the second Time Machine partition you can use Disk Utility to copy the existing Time Machine partition.