Subject: Re: differential scsi controllers
To: None <port-i386@NetBSD.ORG, current-users@NetBSD.ORG, firstname.lastname@example.org,>
From: Thor Lancelot Simon <email@example.com>
Date: 07/01/1998 11:39:15
On Wed, Jul 01, 1998 at 11:15:28AM -0400, Perry E. Metzger wrote:
> "Erik E. Fair" writes:
> > At 13:48 -0700 6/30/98, Michael K. Sanders wrote:
> > >I was asking (on other lists) more for general opinions on the
> > >benefits of differential SCSI, and if mirrored CCDs were 'safe'.
> > Um, I have an open PR on the CCD mirror stuff (kern/3765) - it blew up
> > quite consistently on me on NetBSD/sparc on a sun4m (SPARC Classic).
> > Everyone here reports that the non-mirrored uses of CCD work. I'm actually
> > gearing up to try it again, now that UVM is default on sparc.
> "Don't bother".
> It is known that CCD mirror doesn't work -- I even believe that Jason
> was going to yank it out, because he believes his code isn't worth
> fixing as is. We are now moving towards using RAIDframe for this, or
> so I am told.
It's not Jason's code. It was borrowed from FreeBSD.
Even if it worked, it wouldn't be worth using. It's absolute idiocy --
mirroring for the sake of being able to say you're mirroring. It always
reads from the first component of a mirror set, thus giving no performance
benefit, and it doesn't handle errors *at all*, meaning that an error on
either component will cause the halves of the mirror to become inconsistent,
so that is very unlikely to provide redundancy, either. It's Awful. It
should have been removed Long Ago.