Hammer REDO and other storage notes

Matthew Dillon declared his intention to have REDO working for Hammer very soon.  This will improve speed by lowering the number of fsync()s needed in a given period of time to flush data to disk.

He continues in a separate message talking at length about data flushing and how to implement it efficiently, with some comparisons to work in FreeBSD.  The followups are worth reading, too.