From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Dilger Subject: Re: [PATCH, RFC] mke2fs: get device topology values from blkid Date: Fri, 18 Sep 2009 14:28:14 -0600 Message-ID: <20090918202814.GC2537@webber.adilger.int> References: <4AB2B6B9.7010506@redhat.com> <4AB397F3.3090206@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; CHARSET=US-ASCII Content-Transfer-Encoding: 7BIT Cc: Eric Sandeen , ext4 development To: "Martin K. Petersen" Return-path: Received: from sca-es-mail-2.Sun.COM ([192.18.43.133]:54622 "EHLO sca-es-mail-2.sun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750712AbZIRU2K (ORCPT ); Fri, 18 Sep 2009 16:28:10 -0400 Received: from fe-sfbay-10.sun.com ([192.18.43.129]) by sca-es-mail-2.sun.com (8.13.7+Sun/8.12.9) with ESMTP id n8IKSEMl014985 for ; Fri, 18 Sep 2009 13:28:14 -0700 (PDT) Content-disposition: inline Received: from conversion-daemon.fe-sfbay-10.sun.com by fe-sfbay-10.sun.com (Sun Java(tm) System Messaging Server 7u2-7.04 64bit (built Jul 2 2009)) id <0KQ600500OUVO500@fe-sfbay-10.sun.com> for linux-ext4@vger.kernel.org; Fri, 18 Sep 2009 13:28:14 -0700 (PDT) In-reply-to: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Sep 18, 2009 15:40 -0400, Martin K. Petersen wrote: > >>>>> "Eric" == Eric Sandeen writes: > >> Also, are you guys affected by the > >> previously-acked-sectors-are-now-gone problems with 512-byte > >> logical/4KB physical drives? > > Eric> previously-acked-sectors-are-now-gone? I guess I haven't been > Eric> keeping up. What do you mean by this? > > We already discussed this on irc. But in case anybody else are > wondering... > > On a disk with 4KB physical blocks emulating 512-byte logical blocks the > drive firmware must resort to read-modify-write cycles and that opens up > a new error scenario: > > 4KB physical block: | 0 | > 512b logical block: | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | > ^ ERROR > > In this case we have successfully written LBA 0 - 6. However, when the > drive attempts to write LBA 7 it gets an I/O error and the previous 7 > logical blocks (that have previously been acknowledged as written) are > lost. IOW, the drive write atomicity is at the physical block level and > not the logical ditto. In some sense, this is no worse than "real" sectors 0-6 going bad right after they were written, or in fact even having the writes silently fail. Yes, there is more chance that writing sector 7 (due to 4k sector r-m-w) will cause collateral damage, but the truth even today is that disks are not going to fail a single 512-byte sector at one time, but more likely 64kB (or whatever the remapping unit size is), so this isn't really introducing a new failure mode. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc.