From owner-freebsd-arch@FreeBSD.ORG Wed Dec 30 20:47:53 2009 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 60F2A10656A4; Wed, 30 Dec 2009 20:47:53 +0000 (UTC) (envelope-from xcllnt@mac.com) Received: from asmtpout026.mac.com (asmtpout026.mac.com [17.148.16.101]) by mx1.freebsd.org (Postfix) with ESMTP id 4C37A8FC1F; Wed, 30 Dec 2009 20:47:53 +0000 (UTC) MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; charset=us-ascii Received: from macbook-pro.jnpr.net (natint3.juniper.net [66.129.224.36]) by asmtp026.mac.com (Sun Java(tm) System Messaging Server 6.3-8.01 (built Dec 16 2008; 32bit)) with ESMTPSA id <0KVH00GU5GFRR070@asmtp026.mac.com>; Wed, 30 Dec 2009 12:47:53 -0800 (PST) From: Marcel Moolenaar In-reply-to: <4B39E749.6020502@jrv.org> Date: Wed, 30 Dec 2009 12:47:51 -0800 Message-id: References: <4B349ABF.2070800@FreeBSD.org> <4B39E749.6020502@jrv.org> To: "James R. Van Artsdalen" X-Mailer: Apple Mail (2.1077) Cc: Alexander Motin , FreeBSD-Current , freebsd-arch@freebsd.org Subject: Re: File system blocks alignment X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 30 Dec 2009 20:47:53 -0000 On Dec 29, 2009, at 3:26 AM, James R. Van Artsdalen wrote: > Alexander Motin wrote: >> As we have now mechanism for reporting stripe size and offset for any >> partition to user-level, it should be easy to make disk partitioning and >> file system creation tools to use it automatically. > > Currently all operating systems I know of allocate 128 partition slot > into GPT by default, or 32 blocks. With the dummy MBR and GPT header > added this means that the first partition starts on block 34... > > If FreeBSD is changed to allocate only 120 GPT partition slots by > default then the first partition would begin at block 32. The minimum is 128 partitions as per the EFI/GPT specification. There's no requirement that the partitioned area on the disk follows the GPT header/table in a packed fashion. You can leave a gap. Thus you can have the partitioned area start at sector 64. Note that gpart does not (yet) allow you to do this, but it does respect these parameters when found in the GPT header and won't count the sectors in this gap towards free space. See also the hdr_lba_start & hdr_lba_end fields in struct gpt_hdr. FYI, -- Marcel Moolenaar xcllnt@mac.com