On Tue, Jul 22, 2008 at 02:44:42PM +0200, Dag-Erling Sm??rgrav wrote: > Pawel Jakub Dawidek <pjd_at_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. ZFS does exactly 3. What you are suggesting could be done by not loading geom_mirror.ko module and mounting file system read-only from one of the mirror components. Of course automatic gmirror metadata upgrade is in most of the cases a surprise. Although, one can still just boot it on an older system and create mirror once again - 'gmirror label' command won't touch the data. -- Pawel Jakub Dawidek http://www.wheel.pl pjd_at_FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am!
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