How do I copy a Mac volume using cp? I have researched this for hours. In Single User Mode, I used:

cp -Rpvn /* /Volumes/MyBackup


My external USB is mounted on /Volumes/MyBackup

The issue however is that after 24hrs it still has not stopped copying 300GB of data to an external USB drive. I think it is having issues with symbolic links such as the /Volumes/MacHD volume also having a /Volumes/MacHD and /Volumes/MyBackup I am not sure about this however.

How do I copy a Mac volume using cp? Is cp -Rpvn /* /Volumes/MyBackup correct?
Use rsync for this purpose since cp cannot faithfully reproduce all the files that exist on OS X. The benefits of rsync over ditto and cp are:


interrupted transfers can restart easily with very little cost. 
restarts even resume part way through a large file. 
file exclusion and --dry-run allow easy testing and iterative thinning.


The simplest way to use rsync and preserve most things (permissions, symlinks, edit dates, etc) is to use the -a or --archive flag to archive. To see your progress use -P or --progress

Rsync works as:

rsync options source destination


In your case I would recommend the following:

rsync --archive --verbose --one-file-system --human-readable --progress /from/ /to


Or in short:

rsync -avxhP /from/ /to


Mind the lack of trailing slash in the /to location.

see comments for more useful flags