From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: [md PATCH 15/23] md/raid10 - support resizing some RAID10 arrays. Date: Wed, 14 Mar 2012 19:32:15 +1100 Message-ID: <20120314193215.267f2d83@notabene.brown> References: <20120314043555.7978.75486.stgit@notabene.brown> <20120314044040.7978.69754.stgit@notabene.brown> <20120314061746.GA28196@www5.open-std.org> <20120314172712.3aa9310a@notabene.brown> <4F604E10.20605@westcontrol.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/0JyhhWXt6bDiaKEFlbDSSDK"; protocol="application/pgp-signature" Return-path: In-Reply-To: <4F604E10.20605@westcontrol.com> Sender: linux-raid-owner@vger.kernel.org To: David Brown Cc: keld@keldix.com, linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_/0JyhhWXt6bDiaKEFlbDSSDK Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Wed, 14 Mar 2012 08:51:44 +0100 David Brown wrot= e: > On 14/03/2012 07:27, NeilBrown wrote: > > On Wed, 14 Mar 2012 07:17:46 +0100 keld@keldix.com wrote: > > > >> Hi Neil > >> > >> What is the problem with adding space to the 'far' layout? > >> > >> I would think you could just create the new array part 1 from the > >> old array part 2, and then sync the new array part 2 with the new > >> array part 1. (in the case of a far=3D2 array, for n>2 similar > >> constructs would apply). > > > > If I understand your proposal correctly, you would lose redundancy > > during the process, which is not acceptable. > > >=20 > That's how I understood the suggestion too. And in some cases, that=20 > might be a good choice for the user - if they have good backups, they=20 > might be happy to risk such a re-shape. Of course, they would have to=20 > use the "--yes-I-really-understand-the-risks" flag to mdadm, but other=20 > than that it should be pretty simple to implement. Patches welcome :-) (well, actually not - I really don't like the idea. But my point is that these things turn out to be somewhat more complicated than they appear at first). >=20 > For a safe re-shape of raid10, you would need to move the "far" copy=20 > backwards to the right spot on the growing disk (or forwards if you are=20 > shrinking the array). It could certainly be done safely, and would be=20 > very useful for users, but it is not quite as simple as an unsafe re-size. Reshaping a raid10-far to use a different amount of the device would certainly be possibly, but is far from trivial. One interesting question is how to record all the intermediate states in the metadata. NeilBrown >=20 > mvh., >=20 > David >=20 >=20 > > If I don't understand properly - please explain in a bit more > > detail. > > > > Thanks, NeilBrown > > --Sig_/0JyhhWXt6bDiaKEFlbDSSDK Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) iQIVAwUBT2BXjznsnt1WYoG5AQKwRBAAiVfpLncDTymQU0HcDqKMoBqhxeTkvxz8 UN7/i9s5QzPAENJzjmH06cReITkTeNYUQP4fd1/CZq/mC/mufPCKon6epNcy8EHc nZMlhZLj7oJud2uUtm4Ws2biuc33gyix3XWMHVB0DZFp6aMsKMuly5f+dSXn9cQg ZfpzR4VcSDVow+xWGLM2dxBVQXgzWvpVCHhw4Jdvv/8uh1gTDQwaTOnd4+bRlyGB 62Q+9f5MSfE2CvEGw+pBnUnSXP4n+6WaO2/mI8qOO7kf302UFhcgYieAwNocyzNo uzJ7vv1/HLcJ4BpyYLIVlQKyeNhxb/et5IsuO80hooDhUKsP7sBoozgBWoR6BSsZ da+DFguXl2fRUyGlu2vvCWeVt01hH9tnqWWGfFtDOYZzggVlbD2e/Wl2LDGU1pJg 0ZdrIfdcoHKGgKM1aLb/UAXz9IejXNWKjGqkhdbef4hvgodYbcqzgv9w8P/DSlK4 9SokADYOpcgLXu0HzD4pN0D2oNN++MQLXsrj3jgfS1c1f/n+bM7DprLD5vJ7sZKz T2cxjtoxcNzsI0c3AUamK9cJ5ZFMPJDVldlxF/jYP+AvLFn7I3rNcjOqPZ3NIpIx ZyUXkpqBmJGsQScHygtx5S6j1D0R2NcT8+opOHqlkzTkWQmqua/rUoxuiM3rRjif KzSXQbMTaHo= =ZqG7 -----END PGP SIGNATURE----- --Sig_/0JyhhWXt6bDiaKEFlbDSSDK--