LiveUpdate Administrator 2.x (LUA 2.x) disk space usage is increasing over time, even though purge is enabled and no purge-related errors are reported in the LUA event logs. It seems that the space required by LUA 2.x increases by several GB every month.
Hub set of definitions are full or error sets of definitions received by LUA on monthly basis. The purge settings configured in LUA also apply to these big files (about 3.5GB in total).
This means, for instance, if you configure LUA to keep 5 revisions, you will have up to 5 monthly Hub sets stored on LUA/Distribution Centers.
Reduce the number of revisions to keep in LUA preferences. If the "Purge Updates in Manage Updates Folder" is set to purge "Older than 3 revisions back," then three complete sets of definitions (including hub/full definition sets) will be kept. In many cases, keeping only one past set will be sufficient.
Additional information on how to best tune LUA 2.x for greatest efficiency can be found in the Connect Forum article Managing LiveUpdate Administrator 2.x Space Usage.