When a drive is newly created, it's state is initially set to 'down',
so it won't allow saving the config to it (thus it will never know of
itself being created). Work around this by adding a new flag, that's
also checked when saving the config to a drive.
the previous one failed and there are more than one plex in the volume.
This could have led to a flood of error messages on the console and
probably a deadlock in certain situations.
Analogous to the drive level, give each volume and plex a worker thread
that picks up and processes incoming and completed BIOs.
This should fix the data corruption issues that have come up a few
weeks ago and improve performance, especially of RAID5 plexes.
The volume level needs a little work, though.
