Date: Wed, 25 May 2011 11:37:03 -0600 From: Warner Losh <imp@bsdimp.com> To: Andriy Gapon <avg@FreeBSD.org> Cc: Marcel Moolenaar <xcllnt@mac.com>, freebsd-geom@FreeBSD.org, "Andrey V. Elsukov" <bu7cher@yandex.ru> Subject: Re: [RFC] Remove requirement of alignment to track from MBR scheme Message-ID: <73D4228C-58DF-4A73-A562-34AA4BBF08C4@bsdimp.com> In-Reply-To: <4DDD1C56.70706@FreeBSD.org> References: <4DDA2F0B.2040203@yandex.ru> <D75B2856-D9D8-4BA3-BC54-8258610CEA06@xcllnt.net> <9ED563AB-7B35-40F4-A33E-015317858401@bsdimp.com> <4DDB5375.6050004@FreeBSD.org> <D7C4124D-A690-4960-B141-594C7E2BE792@mac.com> <2FCA1E3C-E11C-46C9-A41B-E5DF4D8BA1FC@bsdimp.com> <9B250685-62F2-4AF7-BDCC-D176FA3C6FCD@mac.com> <4DDD1C56.70706@FreeBSD.org>
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On May 25, 2011, at 9:12 AM, Andriy Gapon wrote: > on 24/05/2011 21:12 Marcel Moolenaar said the following: >> With respect to the creation: >>=20 >> Since out synthesized geometry is not necessarily the same >> as other OSes, we could opt to synthesize a geometry that >> has a track size (=3D sectors/track) that is a multiple of 8 >> (to play nice with 4K sectors), and/or take the stripe >> size of the underlying GEOM into account. This fundamentally >> doesn't change a thing for MBR, but has the side effect of >> achieving some of the goals *and* automatically works for >> EBR as well. >>=20 >> Thus: rather than hack MBR and forgetting about EBR and other >> schemes, maybe we only have to tweak the geometry synthesis >> to give people what they want without going over board.=20 >=20 > I don't think that currently we do synthesize any geometry in kernel. We do. There's at least three cases I can think of. For CAM da = devices, we always synthesize something bogus. For ata devices on pc98 = machines, we create the right fake geometry when certain conditions = require us to create a fake geometry. CAM on pc98 machines also does = this. The disk drives themselves are creating fake geometry and passing it up. > I think that we just whatever BIOS/firmware/etc provides to us in some = way. For MBR and devices > 8GB, this should be ignored, since the fields = saturate (except ones created with our fdisk/sysinstall programs: then = they just size & 0x3ff the values for cylinders rather than the proper = 1023 saturation). >> After >> 9.0 branched, we can do a lot more knowing we have plenty >> of soak time... >=20 > I agree in general, but there is one thing I want now/ASAP - ability = to use gpart > to create (valid) partitions the way I like it disregarding whatever = fake geometry > there might be. I hate when tools go EDAVE on me. At this stage of the game, the boundary checks should be relaxed and = opt-in. We likely should just create MBR slices starting at 64 always, = unless someone has specifically requested that we align things, or asks = for a different starting place. Warner=
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