First step: Create a new repository on your PC or your another server

svnadmin create backup-repository

Second step: Create a hook so as to give the repository the ability to change properties

On Linux/Unix-like

cat <<'EOF' > backup-repository/hooks/pre-revprop-change
#!/bin/sh
exit 0
EOF

Give the newly created file the permission of execution

chmod +w backup-repository/hooks/pre-revprop-change

On Windows

Simply create an empty file named pre-revprop-change.bat in hooks directory (ackup-repository\hooks\pre-revprop-change.bat)

Third step: Initialization the newly created repository

Consult svnsync init --help for more information

On Linux/Unix-like

svnsync init file://`pwd`/backup-repository http://svn.example.com/svn/ource-repository

On Windows

svnsync init file:///c:/full/path/to/backup-repository http://svn.example.com/source-repository

Forth step: Sync them!

svnsync sync file://`pwd`/backup-repository

svnsync sync file:///c:/full/path/to/backup-repository

If you wish, you can hook this command to post-commit hook of the source-repository, with this hook, you will keep you backup-repository up-to-date  

On Windows

On Linux/Unix-like