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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 D3C25C43381 for ; Sat, 16 Feb 2019 05:40:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A66C3222A1 for ; Sat, 16 Feb 2019 05:40:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726882AbfBPFkB (ORCPT ); Sat, 16 Feb 2019 00:40:01 -0500 Received: from ipmail06.adl2.internode.on.net ([150.101.137.129]:50544 "EHLO ipmail06.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725794AbfBPFkB (ORCPT ); Sat, 16 Feb 2019 00:40:01 -0500 Received: from ppp59-167-129-252.static.internode.on.net (HELO dastard) ([59.167.129.252]) by ipmail06.adl2.internode.on.net with ESMTP; 16 Feb 2019 16:09:58 +1030 Received: from dave by dastard with local (Exim 4.80) (envelope-from ) id 1gushh-0000EJ-D0; Sat, 16 Feb 2019 16:39:57 +1100 Date: Sat, 16 Feb 2019 16:39:57 +1100 From: Dave Chinner To: Johannes Thumshirn Cc: lsf-pc@lists.linux-foundation.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-btrfs@vger.kernel.org, hare@suse.de Subject: Re: [LSF/MM TOPIC] Software RAID Support for NV-DIMM Message-ID: <20190216053957.GU20493@dastard> References: <20190215095710.GA12279@linux-x5ow.site> <20190216053133.GT20493@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190216053133.GT20493@dastard> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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... Cheers, Dave. > Cheers, > > Dave. > -- > Dave Chinner > david@fromorbit.com > -- Dave Chinner david@fromorbit.com