of reposotories in the group makes it harder to generate a combination of
key and repository UUID that makes that repository want to contain the key.
+## size balancing
+
+Beyond filtering balanced repos to those that have enough free space to
+store a key, the sizes of the repos can be used in other ways.
+
+If the maximum size of all the balanced repos is known, they can be filled
+with data proportional to their sizes.
+
+If the maximum size is not known of any balanced repos, a reasonable thing
+to do would be to assume they all have the same maximum size, and fill them
+proportionally also.
+
+If the maximum size of some but not others is known, what then?
+
+Balancing this way would fall back to the method above when several repos
+are equally good candidates to hold a key.
+
## stability
Note that this preferred content expression will not be stable. A change in
Also note that "fullybalanced=foo:2" is not currently actually
implemented!
+* implement size-based balancing, either as the default or as another
+ preferred content expression.
+
* `git-annex info` can use maxsize to display how full repositories are
* balanced= and fullybalanced= need to limit the set of repositories to