On a secure network:
- Boot bsd.rd
- Recreate MBR
- Recreate Disklabel
- Start network
For each filesystem:
- newfs(8)
- mount(8)
- cd(1) into filesystem
- make a temp directory for restore (/tmp isn't big enough)
- set TMPDIR to point to that temp directory
- Pipe backup file into restore(8)
- remove the temp directory and the restoresymtable file in the top level directory.
On an insecure network, you need SSH, which is not included in bsd.rd. Either install the OS and reboot before restoring, or use live media.