Drastically reduces the amount of time spent rewriting parity after an
unclean shutdown by keeping better track of which regions might have had
outstanding writes. Enabled by default; can be disabled on a per-set
basis, or tuned, with the new raidctl(8) commands.
Discussed on tech-kern@ to a general air of approval; exhortations to
commit from mrg@, christos@, and others.
Thanks to Google for their sponsorship, oster@ for mentoring the
project, assorted developers for trying very hard to break it, and
probably more I'm forgetting.
