ports/sysutils/rdiff-backup/pkg/DESCR

Rdiff-backup backs up one directory to another, possibly over a network.
The target directory ends up a copy of the source directory, but extra
reverse diffs are stored in a special subdirectory of that target
directory, so you can still recover files lost some time ago. The idea
is to combine the best features of a mirror and an incremental backup.
Rdiff-backup also preserves subdirectories, hard links, dev files,
permissions, uid/gid ownership (if it is running as root), modification
times, acls, eas, resource forks, etc. Finally, rdiff-backup can operate
in a bandwidth efficient manner over a pipe, like rsync. Thus you can
use rdiff-backup and ssh to securely back a hard drive up to a remote
location, and only the differences will be transmitted.