geom_mirror implementation

[Pawel Jakub Dawidek]

On Sun, Nov 09, 2003 at 01:34:50PM -0800, David Schultz wrote:
+> > > > 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.

Raidframe is going to be fixed by scottl at . This is a good news,
but raidframe doesn't fit too good to GEOM infrastructure.
GEOM gives flexibility which is duplicated by RF.

I've start some work on more advance RAID implementation wich should
fit to GEOM just fine. Every RAID level will be a different GEOM class,
but with one configuration utility. All classes will share as many code as
possible to be flexible in adding new RAID levels in futher. Strategy
of choosing disks, failures handle, etc. should be also general. I want to
provide support for many on-disk metadata formats if it will be possible.

The bad news is that it is only a concept, I've only some initial code
and project draft. I hope I'll find time to implement this.

-- 
Pawel Jakub Dawidek                       pawel at dawidek.net
UNIX Systems Programmer/Administrator     http://garage.freebsd.pl
Am I Evil? Yes, I Am!                     http://cerber.sourceforge.net
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