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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: Pawel Jakub Dawidek <pjd@FreeBSD.org>
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Date: Tue, 22 Jul 2008 14:44:42 +0200
In-Reply-To: <20080718070624.GC1976@garage.freebsd.pl> (Pawel Jakub Dawidek's
	message of "Fri\, 18 Jul 2008 09\:06\:24 +0200")
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Cc: Peter Jeremy <peterjeremy@optushome.com.au>,
	Remko Lodder <remko@freebsd.org>, src-committers@freebsd.org,
	"current@freebsd.org" <current@freebsd.org>
Subject: Re: geom_mirror silently upgrading metadata
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Pawel Jakub Dawidek <pjd@FreeBSD.org> writes:
> Just to be clear. I fully agree with you guys. What I could do about
> that when I was working on gmirror (starting from the simplest
> solution):
>
> 1. Skip disks which have version lower then what we have in the kernel.
>
> 2. Upgrade the on-disk metadata automatically.
>
> 3. Make gmirror kernel module to work with all the previous versions and
>    add 'gmirror upgrade' command, so one can upgrade on-disk metadata.

4. Allow an older mirror to be accessed r/o by a newer kernel, side-
   stepping the issue of converting metadata back to the old format.
   Require an explicit 'gmirror upgrade' to upgrade the metadata and
   allow r/w access.

IIRC, this is what ZFS does.  I believe it would be a good compromise
between 2 and 3.

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no