Only calendar sync is configured and is in use. The target db is showing most of data as deleted items.
For example a 200 MB mailbox can show about 30 GB of deleted items.
This is an Exchange 2010 issue. The extreme data bloat could be the result of Exch 2010 Single Item Recovery being enabled and the CalendarVersionStoreDisabled set to 'false' (default setting). Thousands of copies of calendar events are being retained in the RecoverableItems folder in users' mailboxes.
It is a good idea to consult Microsoft when changing the Exchange settings. In this particular case the issue was resolved by correcting the Exchange settings and by setting the CalendarVersionStoreDisabled to 'true' and forcing the ManagedFolderAssistant to run for a given mailbox.