From: Eric Sandeen Subject: Re: [PATCH 0/4] (RESEND) ext3[34] barrier changes Date: Sun, 18 May 2008 21:29:30 -0500 Message-ID: <4830E60A.2010809@redhat.com> References: <482DDA56.6000301@redhat.com> <20080516130545.845a3be9.akpm@linux-foundation.org> <482DF44B.50204@redhat.com> <20080516220315.GB15334@shareable.org> <482E08E6.4030507@redhat.com> <8763tbcrbo.fsf@basil.nowhere.org> <20080519004325.GC8335@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit To: Theodore Tso , Andi Kleen , Eric Sandeen , Andrew Morton , linux-ext4@vger.kernel.org, linux-kernel@ Return-path: Received: from mx1.redhat.com ([66.187.233.31]:55337 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754783AbYESCaK (ORCPT ); Sun, 18 May 2008 22:30:10 -0400 In-Reply-To: <20080519004325.GC8335@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: Theodore Tso wrote: ... > Given how rarely people have reported problems, I think it's a really > good idea to understand what exactly our exposure is for > $COMMON_HARDWARE. I'll propose that very close to 0% of users will ever report "having barriers off seems to have corrupted my disk on power loss!" even if that's exactly what happened. And it'd be very tricky to identify in a post-mortem. Instead we'd probably see other weird things caught down the road during some later fsck or during filesystem use, and then suggest that they go check their cables, run memtest86 or something... Perhaps it's not the intent of this reply, Ted, but various other bits of this thread have struck me as trying to rationalize away the problem. If the discussion were about proper locking to avoid corruption, would we really be saying well, gosh, it's a *really* small window, and *most* people won't hit it very often, and proper locking would slow things down.... So I think that as you suggest, looking for ways to make barriers less painful is the far better route, rather than sacrificing correctness for speed by turning them off by default when we know there is a chance for problems. People running journaling filesystems most likely expect to be safe from this sort of thing, not most of the time, but all of the time. -Eric