From owner-freebsd-questions@FreeBSD.ORG Thu Nov 15 15:44:20 2012 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id EF42B1FC for ; Thu, 15 Nov 2012 15:44:20 +0000 (UTC) (envelope-from wblock@wonkity.com) Received: from wonkity.com (wonkity.com [67.158.26.137]) by mx1.freebsd.org (Postfix) with ESMTP id 8DCAE8FC08 for ; Thu, 15 Nov 2012 15:44:20 +0000 (UTC) Received: from wonkity.com (localhost [127.0.0.1]) by wonkity.com (8.14.5/8.14.5) with ESMTP id qAFFiJrX063126; Thu, 15 Nov 2012 08:44:19 -0700 (MST) (envelope-from wblock@wonkity.com) Received: from localhost (wblock@localhost) by wonkity.com (8.14.5/8.14.5/Submit) with ESMTP id qAFFiFgw063123; Thu, 15 Nov 2012 08:44:19 -0700 (MST) (envelope-from wblock@wonkity.com) Date: Thu, 15 Nov 2012 08:44:15 -0700 (MST) From: Warren Block To: "Ronald F. Guilmette" Subject: Re: Advanced Format Drive ? In-Reply-To: <21828.1352983292@tristatelogic.com> Message-ID: References: <21828.1352983292@tristatelogic.com> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (wonkity.com [127.0.0.1]); Thu, 15 Nov 2012 08:44:19 -0700 (MST) Cc: freebsd-questions@freebsd.org X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 15 Nov 2012 15:44:21 -0000 On Thu, 15 Nov 2012, Ronald F. Guilmette wrote: > In your tutorial document, you say: > > "Create a boot partition to hold the loader, size of 512K." > > How big is that thing (gpart boot loader), actually? Half a megabyte > seems rather a bit large-ish, certainly relative to ye olde MBR loader, > which I gather was limited to... what? 32KB (minus a little for the > partition table) ? /boot/gptboot is 15K, /boot/gptzfsboot is 39K. A code limitation makes 512K the largest this partition can be made. So I make it that big so it won't have to be increased for bigger boot loaders later. And the space is not wasted because of the next partition... > Also, when creating the partition to hold the GPT boot loader, shouldn't > that "gpart add" operation include a "-b 4k" option, you know, on a > modern "Advanced Format" disk? If not, why not? -a 4k, yes. It doesn't really matter. The loader is read only at boot, once, and it's tiny. So it doesn't really matter if it reads at 30M/second or 500M/second. But yes, for consistency, I'll modify that so the start of the freebsd-boot partition is at 40. > You also go on to say: > > "Create partition for /. It should start at the 1M boundary for proper > sector alignment on 4K sector drives." > > Come again? Sorry, but you just lost me entirely. In order to get "proper > sector alignment" on one of these newer Advanced Format (4k) drives, why > on earth should it be necessary to begin a partition at some alignment > which is greater than the obvious minimum, i.e. 4KB ? Starting the first filesystem partition at 1M is a semi-standard, used by various vendors including Microsoft. Besides being aligned to 4K, it's also aligned to bigger values that can be important for performance on devices like SSDs. And that explains the oversized boot partition. It's space that would be unused otherwise.