From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ipmail06.adl2.internode.on.net (ipmail06.adl2.internode.on.net [150.101.137.129]) by ml01.01.org (Postfix) with ESMTP id 6E933208EB3E4 for ; Fri, 15 Feb 2019 21:39:59 -0800 (PST) Date: Sat, 16 Feb 2019 16:39:57 +1100 From: Dave Chinner 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-Disposition: inline In-Reply-To: <20190216053133.GT20493@dastard> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Johannes Thumshirn Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, hare@suse.de, linux-fsdevel@vger.kernel.org, lsf-pc@lists.linux-foundation.org, linux-btrfs@vger.kernel.org List-ID: 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 _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm