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=-1.0 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED 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 3F776C43381 for ; Sat, 16 Feb 2019 17:05:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 033F42192B for ; Sat, 16 Feb 2019 17:05:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="RlvZGdI0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726084AbfBPRFn (ORCPT ); Sat, 16 Feb 2019 12:05:43 -0500 Received: from mail-ot1-f66.google.com ([209.85.210.66]:41377 "EHLO mail-ot1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726229AbfBPRFn (ORCPT ); Sat, 16 Feb 2019 12:05:43 -0500 Received: by mail-ot1-f66.google.com with SMTP id t7so5401109otk.8 for ; Sat, 16 Feb 2019 09:05:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=E5oU+8OGWfNcbFFs3SOhhw6G8UO44WCYyxqkkn/iCiA=; b=RlvZGdI0Xmjp/x40FV4IXDsNu9zn/tpczpkPTwGMfS4SNYVlks8zEf7KNUteuPEjky FEhikT7DFgVH1xK2raUXdRoYjNKvUQFrbdIWIZ5gJu09Ee4JtcpZSIH/M+8iVmZAC4q7 IP/T+JoQDg+qHDt3Rsl4PmcsndDrg67EoHjjw5coPqgU1cWChSTjTEfG8gGxmKWL7pqH /Dqbhk706Ox5wbz4oGHnDAV50W+VZ8nf104P1dLD/rq0qzJIxc4w+sqMoL7ynLBVm/SC WyCqXw0Q15tI9esePgb+ItKYXFkB3IVvJbcLjlkGDiKB/41voQhpTVJ1QoVBV+I6FG+g GrdQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=E5oU+8OGWfNcbFFs3SOhhw6G8UO44WCYyxqkkn/iCiA=; b=UJnlJeW3Mc4X/S0F9e8sz3QgleNpo3e86vRm6Jfa+QElZ1RR49p2OHHcGQC2lkneW4 fLKuQuzrBnqqDXUqvNVVrY0UBH9kwd4hobmNco/ci1ueFtNCyG84VhtuQs5h4FwO8Idj 6cWOsHYFXVjuGym+NEkZv1rQX33X2Ib7vt69ZujY60zJDLvX62vmQMiu2ipuvb4xha8a bvJJs+XII26FlYXx5EfAOYyTE9WFNsDTYrUZyYuMEYLkygYJ3Uj74tNcwEwqhhR2rqNY ++DBasqr3rTtzbUaNelU5qcBQjbR/49lNOflV2sCtEXFfiBXQHWNx6rfTDzsoM/FXIlV Us/Q== X-Gm-Message-State: AHQUAuYPn6kQwg+YrJsNQSggormTODJriFOpXZTAjiaEeLKh3HwVmYh0 BHj5s1xtR5K47Ie7q5+kXBi0BFh9xzfB01GNJaJbdA== X-Google-Smtp-Source: AHgI3IYyZ0wumcjTfYgSq+CjMP8M0nxipsFzA4By+4DUlvx6zlqWN11pOaw6lB7UQ8w9nbAjUtxGhgyT+MnbAKjrpZw= X-Received: by 2002:aca:cc0f:: with SMTP id c15mr10317703oig.105.1550336742379; Sat, 16 Feb 2019 09:05:42 -0800 (PST) MIME-Version: 1.0 References: <20190215095710.GA12279@linux-x5ow.site> <20190216053133.GT20493@dastard> <20190216053957.GU20493@dastard> In-Reply-To: <20190216053957.GU20493@dastard> From: Dan Williams Date: Sat, 16 Feb 2019 09:05:31 -0800 Message-ID: Subject: Re: [LSF/MM TOPIC] Software RAID Support for NV-DIMM To: Dave Chinner Cc: Johannes Thumshirn , linux-nvdimm , linux-block@vger.kernel.org, Hannes Reinecke , linux-fsdevel , lsf-pc@lists.linux-foundation.org, linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Feb 15, 2019 at 9:40 PM Dave Chinner wrote: > > On Sat, Feb 16, 2019 at 04:31:33PM +1100, Dave Chinner wrote: > > On Fri, Feb 15, 2019 at 10:57:12AM +0100, Johannes Thumshirn wrote: > > > (This is a joint proposal with Hannes Reinecke) > > > > > > Servers with NV-DIMM are slowly emerging in data centers but one key feature > > > for reliability of these systems hasn't been addressed up to now, data > > > redundancy. > > > > > > While it would be best to solve this issue in the memory controller of the CPU > > > itself, I don't see this coming in the next few years. This puts us as the OS > > > in the burden to create the redundant copies of data for the users. > > > > > > If we leave of the DAX support Linux' software RAID implementations (MD, > > > device-mapper and BTRFS RAID) do already work on top of pmem devices, but they > > > are incompatible with DAX. > > > > > > In this session Hannes and I would like to discuss eventual ways how we as an > > > operating system can mitigate these issues for our users. > > > > We've supported this since mid 2018 and commit ba23cba9b3bd ("fs: > > allow per-device dax status checking for filesystems"). That is, > > we can have DAX on the XFS RT device indepently of the data device. > > > > That is, you set up pmem in three segments - two small identical > > segments start get mirrored with RAID1 as the data device, and > > the remainder as a block device that is dax capable set up as the > > XFS realtime device. Set the RTINHERIT bit on the root directory at > > mkfs time ("-d rtinherit=1") and then all the data goes to the DAX > > capable realtime device, and all the metadata goes to the software > > raided pmem block devices that aren't DAX capable. > > > > Problem already solved, yes? > > Sorry, this was meant to be a reply to Dan's email commenting about > some people needing mirrored metadata, not the parent that was > talking about whole device RAID... > > i.e. mirrored metadata w/ FS-DAX for data should already be a solved > problem... Ah true, thanks for the clarification. I'll give it a try, the last time I looked RT configurations failed with DAX, but perhaps that's been fixed and I can drop if from my list of broken DAX items.