Packing a Subversion repository will only provide minimal space savings; all it's doing is combining sharded revisions into a single file.
If there is space to be reclaimed, it will be because you have revisions which can be made smaller via rep sharing or better diffing/compression that was introduced in newer versions of Subversion. This assumes that you have a long history that you created with an older version of the server and have upgraded over time; older versions will be "bigger" than newer ones.
The only way to retroactively take advantage of those improvements is to "rebuild" the repository completely with the current version. You can do this in one of two ways:
- Perform an svnadmin dump/load cycle, as described in the manual. You'll be "migrating" the repository from and to the same server, but the principle is the same.
- Create a new repository, use
svnsync
to push everything into it, then remove the old one and attach the new one in the location where you're currently serving the repository. You'll have some extra work to do with permissions & hook scripts.
Of course, you need to be sure that you have solid backups before attempting either method.