From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5BA75C4646D for ; Sat, 4 Aug 2018 05:20:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 09CCB21775 for ; Sat, 4 Aug 2018 05:20:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=thunk.org header.i=@thunk.org header.b="p3Di7WUO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 09CCB21775 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=mit.edu Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727832AbeHDHUF (ORCPT ); Sat, 4 Aug 2018 03:20:05 -0400 Received: from imap.thunk.org ([74.207.234.97]:36424 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726186AbeHDHUF (ORCPT ); Sat, 4 Aug 2018 03:20:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=thunk.org; s=ef5046eb; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=eyRbIOy++1SQ0QjOX3jJd/TSPjlUqCYZr6nuf+XihHQ=; b=p3Di7WUO6bpaR95m4UW2V0wFnF q8Sf/sfxOeZr4ON0tHvb45TrC5qAVvmYDrGQAsGxuGPa3lBWDlpwLwq7Qn+ErQ37diH86KBOGv/Dz pSYvytdycsOWQIgnQFJFMmaZLgLSGLZmpSQjKm88JTK0dLZ5ECX++w6M7uk/IHhBRJds=; Received: from root (helo=callcc.thunk.org) by imap.thunk.org with local-esmtp (Exim 4.89) (envelope-from ) id 1flozS-0007xW-7p; Sat, 04 Aug 2018 05:20:34 +0000 Received: by callcc.thunk.org (Postfix, from userid 15806) id 4EB607A64C9; Sat, 4 Aug 2018 01:20:33 -0400 (EDT) Date: Sat, 4 Aug 2018 01:20:33 -0400 From: "Theodore Y. Ts'o" To: Mike Snitzer Cc: Linus Torvalds , Jens Axboe , Sagi Grimberg , Linux Kernel Mailing List , linux-block , dm-devel@redhat.com, Zdenek Kabelac , Ilya Dryomov , wgh@torlan.ru Subject: Re: [dm-devel] LVM snapshot broke between 4.14 and 4.16 Message-ID: <20180804052033.GA4461@thunk.org> Mail-Followup-To: "Theodore Y. Ts'o" , Mike Snitzer , Linus Torvalds , Jens Axboe , Sagi Grimberg , Linux Kernel Mailing List , linux-block , dm-devel@redhat.com, Zdenek Kabelac , Ilya Dryomov , wgh@torlan.ru References: <1ec0a220-d5b0-1c27-e63b-c4d3f4ce9d77@torlan.ru> <20180803185431.GB3258@redhat.com> <20180803193037.GA4581@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180803193037.GA4581@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 03, 2018 at 03:30:37PM -0400, Mike Snitzer wrote: > > I was trying to give context for the "best to update lvm2 anyway" > disclaimer that was used. Yeah, it was specious. Well, it seemed to indicate a certain attitude that both Linus and I are concerned about. I tried to use more of a "pursuading" style to impress why that attitude was not ideal/correct. Linus used a much more assertive style (e.g., "Hell, no!"). > And yeah, that isn't a good excuse to ignore it but: dm-snapshot is a > steaming pile as compared to dm thin-provisioning... On a side note, this is the first that I've heard the assertion that dm-thin was better than dm-snapshot. My impression was that dm-snapshot was a proven code base, that only did one thing and (as far as I could tell) did it well. In contrast, dm-thin is much newer code, **far** more complex, with functionality and corner cases approaching that of a file system --- and just to be even more exciting, it doesn't have an fsck/repair tool to deal with corrupted metadata. In your opinion, is it because you disagree with the assumption that dm-thin is scary? Or is the argument that dm-snapshot is even scarier? - Ted P.S. It could be that my impression is wrong/out-dated, but the kernel documentation still says that userspace tools for checking and repairing the metadata are "under development". As a file system developer, the reaction this inspires is best summed up as: https://imgflip.com/memetemplate/50971393/Scared-Face