Every few seconds (you may define how many) journal is terminated and
marked as consistent and gjournal starts to copy data from it to the
data provider. In the same time new data are stored in new journal.
Let's call the moment in which journal is terminated as "journal switch".
Journal switch looks as follows:
1. Start journal switch if we have timeout or if we run out of cache.
   Don't perform journal switch if there were no write requests.
2. If we have file system, synchronize it.
3. Mark file system as clean.
4. Block all write requests to the file system.
5. Terminate the journal.
6. Eventually wait if copying of the previous journal is not yet
   finished.
7. Send BIO_FLUSH request (if the given provider supports it).
8. Mark new journal position on the journal provider.
9. Unblock write requests.
10. Start copying data from the terminated journal to the data provider.