Date: Wed, 27 Jun 2012 20:34:47 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Marcel Moolenaar <marcel@xcllnt.net> Cc: freebsd-current <freebsd-current@FreeBSD.org>, freebsd-hackers <freebsd-hackers@FreeBSD.org>, "Andrey V. Elsukov" <bu7cher@yandex.ru>, Andriy Gapon <avg@FreeBSD.org>, Kevin Oberman <kob6558@gmail.com> Subject: Re: [CFC/CFT] large changes in the loader(8) code Message-ID: <20120627183446.GC1401@garage.freebsd.pl> In-Reply-To: <E5F4BCA6-8AEF-40C2-B44A-D2050069D0A7@xcllnt.net> References: <4FE9B01C.30306@yandex.ru> <201206261337.11741.jhb@freebsd.org> <20120626212308.GE1399@garage.freebsd.pl> <CAN6yY1vBSPjeP6HzuH4ityRhguGhi-b9Nd=YRfyAtfNZaNSC7A@mail.gmail.com> <20120626214330.GG1399@garage.freebsd.pl> <E5F4BCA6-8AEF-40C2-B44A-D2050069D0A7@xcllnt.net>
next in thread | previous in thread | raw e-mail | index | archive | help
--p2kqVDKq5asng8Dg Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Jun 27, 2012 at 10:45:35AM -0700, Marcel Moolenaar wrote: >=20 > On Jun 26, 2012, at 2:43 PM, Pawel Jakub Dawidek wrote: > >=20 > > As for sharing disk with other OS. If you share the disk with OS that > > doesn't support gmirror, you shouldn't use gmirror in the first place. > > You probably want to use only formats that are recognized by all your > > OSes. >=20 > This statement is ridicuous by virtue of not being in touch with > reality and by making gmirror useless for such wide range of cases > that one can question why we have it at all. >=20 > Put differently: a mirroring class is a fairly basic and useful thing > to have. Limiting it's use is nothing but artificial and follows from > having to use the underlying provider to store metadata. This then > changes the view of the underlying providing to consumers above gmirror > in a way that makes the presence or absence of gmirror visible. > Solving the visibility problem makes gmirror useful all the time. > I see that as a better way of looking at it than simply blurting out > that you shouldn't use gmirror when certain awkward and artifical > conditions apply. I'm sorry, Marcel, but what you describe here has nothing to do with reality. To be able to implement realiable mirroring you have to use on-disk metadata. There is no way around that. You can implement non-redundant GEOM classes without using on-disk metadata, but out-of-band configuration in case of mirroring is simply naive. How do you detect that components are out of sync, for example? And when it comes to visablity. Are you suggesting that gmirror should present entire underlying provider to upper layers? Including its metadata? I hope not, because we went through that hell already (remember skipping first 16 sectors by UFS, as BSDlabel metadata might be there? The same for swap?). I think I did pretty good job by making the metadata as simple as possible - I use exactly one sector at the end of the target device. I'm really having a hard time to think of a simpler format. --=20 Pawel Jakub Dawidek http://www.wheelsystems.com FreeBSD committer http://www.FreeBSD.org Am I Evil? Yes, I Am! http://tupytaj.pl --p2kqVDKq5asng8Dg Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAk/rUkYACgkQForvXbEpPzQMtgCZAREkUfa4bpLIFZc7sfKY87Vu 6hcAoLp8W6xgJg6eViZG1ZU3RXsvEgrC =ZREU -----END PGP SIGNATURE----- --p2kqVDKq5asng8Dg--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20120627183446.GC1401>