From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: ATA 4 KiB sector issues. Date: Tue, 16 Mar 2010 06:24:57 -0700 Message-ID: <1268745897.21384.14.camel@mulgrave.site> References: <4B947393.2050002@kernel.org> <201003100046.24695.arnd@arndb.de> <1158166a1003100114j6ea329fbh84bfad65dcac90bf@mail.gmail.com> <4B9EED55.10201@kernel.org> <1268720060.21384.10.camel@mulgrave.site> <4B9F2388.2030803@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from cantor.suse.de ([195.135.220.2]:59721 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966007Ab0CPNZN (ORCPT ); Tue, 16 Mar 2010 09:25:13 -0400 In-Reply-To: <4B9F2388.2030803@kernel.org> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Tejun Heo Cc: Denys Vlasenko , Arnd Bergmann , "linux-ide@vger.kernel.org" , lkml , Daniel Taylor , Jeff Garzik , Mark Lord , tytso@mit.edu, "H. Peter Anvin" , hirofumi@mail.parknet.co.jp, Andrew Morton , Alan Cox , irtiger@gmail.com, Matthew Wilcox , aschnell@suse.de, knikanth@suse.de, jdelvare@suse.de On Tue, 2010-03-16 at 15:22 +0900, Tejun Heo wrote: > Hello, James. > > On 03/16/2010 03:14 PM, James Bottomley wrote: > > So, it is true to say that picking a certain H/S geometry (which is > > entirely withing the gift of the partitioner) will align msdos label > > partitions, but will be don't care for all other labels: all other > > partition labels (like gpt) use block as offset and don't have any truck > > with the fictitious C/H/S stuff. > > For any modern Linux and Windows, CHS simply doesn't matter. They > don't look at it at all. If they have a msdos label, they do. > > The big problem is that 99% of the x86 systems out there still use the > > ancient msdos label for their boot disks, so aligning H/S going forwards > > will give us a nice "just works" for x86 boxes. > > What I don't get is that how picking up a custom geometry can make > things work when there is *no* reliable way to determine which > geometry was used during partitioning once the partitioning is > complete. For msdos labels, it's embedded in the label ... for all other labels, it's made up on the spot. > Most BIOSs these days will simply report the geometry as > being 255/63 regardless of the geometry used during partitioning. So, > how can using a custom geometry give that nice "just works" for x86 > boxes when nobody knows what geometry is in use? Because the msdos label can only partition in units of cylinders. If you're using an msdos label, picking the right H/S gets you alignment. James