On Wed, Jun 27, 2012 at 08:22:25AM -0400, John Baldwin wrote:
> > I don't think so. Most common case is to configure partitions on top of
> > a mirror. Mirroring partitions is less common. Mostly because of
> > hardware RAIDs being popular. You don't expect hardware RAID vendor to
> > mirror partitions. Partition editors for other OS's won't work, but only
> > because they don't support gmirror. If they wouldn't recognize and
> > support some hardware (or pseudo-hardware) RAIDs there will be the same
> > problem.
> Hardware RAIDs hide the metadata from the disk that the BIOS (and disk
> editors) see.  Thus, putting a GPT on a hardware RAID volume works fine
> as the logical volume is always seen by all OS's consistently. [...]

Only if you won't connect this disk to a different controller.

> [...] The same
> is even true of the "software" RAID that graid supports since the metadata
> is defined by the vendor and thus the logical volume is always seen other
> OS's consistently.

But is it seen without metadata by the boot loader?

What I'm trying to say is that it is fair to expect from the user to not
use gmirror-configured disk on different OS. If the user wants to use
this disk in different OS then he has to use format that is recognized
by both.

Because gmirror is supported by FreeBSD we should improve the support by
teaching boot loader about it. Pretending gmirror is special and
recommending to mirror partitions with it instead of raw disks is not
the solution.

I really can't see how gmirror is different in this regard from any
other software RAID or volume manager. If you try to use disk that
contains unrecognized metadata the behaviour is undefined (but hopefully
not a panic).

Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
Am I Evil? Yes, I Am!                     http://tupytaj.pl

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