geom_mirror implementation

[David Schultz]

On Sun, Nov 09, 2003, Christian Laursen wrote:
> David Schultz <das at FreeBSD.ORG> writes:
> 
> > On Sun, Nov 09, 2003, Lukas Ertl wrote:
> > > Hi hackers@,
> > > 
> > > I've played around with GEOM a bit and beefed up geom_mirror, which is
> > > already in the tree but not built yet.
> > > 
> > > You can find the patch at <http://mailbox.univie.ac.at/~le/geom.diff>.
> > 
> > Hmm...I believe geom_mirror is supposed to be an example, and
> > geom_ccd is supposed to be the production mirroring implementation.  
> > ccd does have its quirks, though...
> 
> Last time I checked ccd needed to be manually reconfigured to run in
> degraded mode and sync is not possible. In my book that's not good
> enough for production.
> 
> Furthermore it would be nice with a mirror implementation that
> automatically syncs the mirror after an unclean shutdown.

Yeah, RAID support in FreeBSD is in a rather sorry state right
now.  ccd(4) doesn't work with ATAng on my machine without causing
panics and data corruption, raidframe is broken in -CURRENT, and
vinum tends to lag behind changes and break.  But that doesn't
mean that the right solution is to add a *fourth* incompatible
RAID implementation.  If there's a good reason ccd(4) is harder to
fix than geom_mirror, then you might want to talk to phk about
rewriting geom_ccd based on geom_mirror.  I believe scottl and phk
have plans to fix raidframe, though, which would address a lot of
the present limitations.