geom_mirror silently upgrading metadata

[Dag-Erling Smørgrav]

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.

DES
-- 
Dag-Erling Smørgrav - des at des.no