From owner-freebsd-questions Tue Jan 14 11:36:50 2003 Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 0F77537B401 for ; Tue, 14 Jan 2003 11:36:48 -0800 (PST) Received: from salmon.maths.tcd.ie (salmon.maths.tcd.ie [134.226.81.11]) by mx1.FreeBSD.org (Postfix) with SMTP id E3E8B43F43 for ; Tue, 14 Jan 2003 11:36:46 -0800 (PST) (envelope-from iedowse@maths.tcd.ie) Received: from walton.maths.tcd.ie by salmon.maths.tcd.ie with SMTP id ; 14 Jan 2003 19:36:38 +0000 (GMT) To: swear@attbi.com Cc: Mike Meyer , freebsd-questions@freebsd.org Subject: Re: Dangerously dedicated vs. fully dedicated, etc. In-Reply-To: Your message of "14 Jan 2003 11:01:36 PST." Date: Tue, 14 Jan 2003 19:36:37 +0000 From: Ian Dowse Message-ID: <200301141936.aa93359@salmon.maths.tcd.ie> Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In message , swear@attbi.com writes: >Mike, I'll pay back your effort in replying to this long thing by >working up a patch for the "disklabel" manpage (at least) and, if you >want, I'll CC you so you can veto things you don't like. I do worry At the risk of adding to the confusion, here is a less wordy description of the various disk layouts. The term `dangerously dedicated' seems to be used to refer to either options (B) or (C), so I will avoid using that term: (A) Normal sliced disk (assuming sectors/track = 63) sector 0: boot0 and the DOS slice table sectors 1..62: unused sector 63: boot1 sector 64: disklabel sectors 65-78: boot2 sectors 79-92: 'a' partition filesystem superblock Note that the disklabel, which contains a list of the partitions within a slice is actually contained within the space allocated to the first partition. To ensure that this does not get clobbered by the filesystem, the first 8k of every ffs filesystem is reserved for boot code and the disklabel. (B) Dedicated format created by sysinstall sector 0: boot1 and the DOS slice table, where the slice table contains one slice (slice 1) covering the entire disk, including sector 0. sector 1: disklabel sector 2-15: boot2 sectors 16-31: 'a' partition filesystem superblock In this case, there is no boot0, and boot1 serves as the boot loader that is invoked by the BIOS. Here, all of the boot code is contained within the first slice and also within the first partition. Again, the 8k reserved at the start of every ffs filesystem protects the boot code. Sysinstall sets up fstab to refer to the partitions as e.g. /dev/ad0s1a (I think). (C) Dedicated format using dummy slice sector 0: boot1 and the DOS slice table. The slice table contains a single entry (slice 4) that starts at sector 0 and has a size of 50000 sectors, whatever the real disk size is. sector 1: disklabel sector 2-15: boot2 sectors 16-31: 'a' partition filesystem superblock This is like (B) except that slice 4 instead of slice 1 is used, and the size of the slice in the slice table is bogus. The partitions on such a disk are usually accessed using the compatibility slice names such as /dev/ad0a. Ian To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message