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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4631FC433F5 for ; Tue, 1 Mar 2022 11:09:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=j+v40RHPB1UVEqMJ0EcbkvBgS+le4AGmKV5CwY9Ny2k=; b=s93u3VOJI7JhCyPK8ot5/HgVqL Dwvs3g3DXwO/Ic3XbqLk7r4ltWWCESjYN0A7aaEO6DuSDljH7lOxsakh056nlfXziLYtFyf4teMtR Wrx/119L39Ion+tyyva61gfPDytxHlEyYJPDjBmirf9ozuA1pgWbi3+vEYPRn+WwYIJxy/COPv4bB KdM8oD39weOZGhOTSMKxFutfgOJqdb79b3U/uFmBjXCLWUDbKbDlzumPG8CVhsvrql2V1GXRRWp+k qZ8CoeHwEUvcwvqsvhlil48m7OF1L0OWWdlZj3Lky5ajzIldg2hapY9zkIZzLxdIIg4dgATX0OrUY kysPPCPQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nP0O2-00GLY8-PS; Tue, 01 Mar 2022 11:09:46 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nP0NH-00GLGA-7t for linux-nvme@lists.infradead.org; Tue, 01 Mar 2022 11:09:01 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id ED29068AFE; Tue, 1 Mar 2022 12:08:40 +0100 (CET) Date: Tue, 1 Mar 2022 12:08:40 +0100 From: Christoph Hellwig To: Randy Jennings Cc: Christoph Hellwig , Keith Busch , linux-nvme@lists.infradead.org, Prabhath Sajeepa , Jens Axboe , Sagi Grimberg , Uday Shankar Subject: Re: Native multipath across multiple subsystem NQNs Message-ID: <20220301110840.GA2005@lst.de> References: <20220211220714.GA370236@dev-ushankar.dev.purestorage.com> <20220212063422.GA16561@lst.de> <20220212212221.GB1660900@dhcp-10-100-145-180.wdc.com> <20220214081252.GA18231@lst.de> <20220225001547.GA3454995@dev-ushankar.dev.purestorage.com> <20220225005306.GA904231@dev-randyj2.dev.purestorage.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220225005306.GA904231@dev-randyj2.dev.purestorage.com> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220301_030859_495736_D0106571 X-CRM114-Status: GOOD ( 19.83 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Thu, Feb 24, 2022 at 05:53:06PM -0700, Randy Jennings wrote: > In addition to other considerations, migrating a namespace with hot data > from a different storage vendor array nondisruptive to client i/o would > be difficult to do without having a namespace exist under multiple NQNs. > One approach that has been used for SCSI is by multipathing to both > targets & a proxy mirroring writes; on cut-over, the other path > disconnects. If the filehandle has to change, that is disruptive to the > client software. > > Unifying different storage arrays behind the same NQN/virtual subsystem > requires coordination of nvme ctrl_ids at least, and doing that between > different storage vendor arrays is unlikely. Having a mechanism to > migrate between different JBOF devices non-disruptively would be helpful > regardless of the source/destination vendors. Such devices will > probably not have the option of virtual subsystems. Yes, it does require coordination, so please coordinate. > In other words, even with implementing virtual subsystems, we still have > use for non-disruptively moving a namespace between subsystems. How > will this usecase be supported on Linux? You can create a mirror using dm (or md but not as easily), resync and then cut off a leg. If you want to do that transparently on an already existing device node you'll need to pick up the block device interposer patchset and help to get it upstream.