Found this post over at EAB that mfilos answered and thought I’d make a copy for easy reference:

Just open a CLI and type:

1> DH0:
1> lha -aezrx a DH1:backup.lha #?

That will create a file called “backup.lha” under partition DH1 (assuming the partition you want to backup is partition DH0) maintaining all protection bits etc.
The archive is not compressed so it will be rather large. If you want to make it compressed also just replace “z” with “Z” in lha options of the command provided.
Then of course you can transfer the one lha file via FTP or any other way anywhere

To restore the archive anytime just use the following command:

1> DH0:
1> lha x DH1:backup.lha