A backup by necessity is a copy; with centralized version control as svn is, you don't have a copy of the repository, so you have to make one some way.

(Decentralized version control is only slightly different; if you lose the 'main' repository and don't have an exact clone (aka a backup), you may be able to glue together something from other repositories that is close to or equal to what you had, but there is no way to know for sure)