Comment 1 for bug 1220269

Details from a (different charm's) unit, showing the same issue:
root@foo-machine-4:/var/lib/juju/agents/unit-foo-0/state/deployer# du -sch *
4.0K current
787M update-20130815-190344257582687
264M update-20130815-192344262960692
265M update-20130815-194339086464813
4.5M update-20130815-200434891456026
264M update-20130823-022039017985439
265M update-20130823-024104022903924
264M update-20130823-030044303670381
265M update-20130823-032050241864282
264M update-20130823-034120180909899
265M update-20130823-040045833427856
264M update-20130823-042045032793529
265M update-20130823-044040198995862
264M update-20130823-050110056499511
265M update-20130823-052045733940204
264M update-20130823-054055034454853
265M update-20130823-060055131687442
264M update-20130823-062056093227875
265M update-20130823-064051274967432
264M update-20130823-070046575347985
265M update-20130823-072046676001742
264M update-20130823-074046557291471
265M update-20130823-080051964571236
264M update-20130823-082051047332637
265M update-20130823-084057056244426
231M update-20130823-090052010815611
6.7G total

* can clearly see the one-per-20min update frequency (it's cron-ed to be so)
* directory size matches charm size (it carries a ~260M .tgz code payload)