From: Ted Ts'o Subject: Re: [dm-devel] Ext4 and xfs problems in dm-thin on allocation and discard Date: Tue, 19 Jun 2012 15:58:34 -0400 Message-ID: <20120619195834.GC22805@thunk.org> References: <4FDF9EBE.2030809@shiftmail.org> <20120619141933.GC10637@thunk.org> <20120619144316.GD14208@agk-dp.fab.redhat.com> <20120619152856.GB7225@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: =?utf-8?B?THVrw6HFoQ==?= Czerner , linux-ext4@vger.kernel.org, xfs@oss.sgi.com, Spelic To: device-mapper development Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:51372 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753101Ab2FST6k (ORCPT ); Tue, 19 Jun 2012 15:58:40 -0400 Content-Disposition: inline In-Reply-To: <20120619152856.GB7225@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Jun 19, 2012 at 11:28:56AM -0400, Mike Snitzer wrote: > > That is an lvm2 BZ but there is further kernel work needed. > > It should be noted that the "external origin" feature was added to the > thinp target with this commit: > http://git.kernel.org/linus/2dd9c257fbc243aa76ee6d > > It is start, but external origin is kept read-only and any writes > trigger allocation of new blocks within the thin-pool. Hmm... maybe this is what I had been told. I thought there was some feature where you could take a read-only thinp snapshot of an external volume (i.e., a pre-existing LVM2 volume, or a block device), and then after that, make read-write snapshots using the read-only snapshot as a base? Is that something that works today, or is planned? Or am I totally confused? And if it is something that works today, is there a web site or documentation file that gives a recipe for how to use it if we want to do some performance experiments (i.e., it doesn't have to be a user friendly interface if that's not ready yet). Thanks, - Ted