From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id q5JKia85161806 for ; Tue, 19 Jun 2012 15:44:37 -0500 Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by cuda.sgi.com with ESMTP id OAHvvZVNxWcOBZL8 for ; Tue, 19 Jun 2012 13:44:36 -0700 (PDT) Date: Tue, 19 Jun 2012 16:44:28 -0400 From: Mike Snitzer Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard Message-ID: <20120619204428.GA9485@redhat.com> References: <4FDF9EBE.2030809@shiftmail.org> <20120619141933.GC10637@thunk.org> <20120619144316.GD14208@agk-dp.fab.redhat.com> <20120619152856.GB7225@redhat.com> <20120619195834.GC22805@thunk.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20120619195834.GC22805@thunk.org> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Ted Ts'o Cc: =?utf-8?B?THVrw6HFoQ==?= Czerner , device-mapper development , linux-ext4@vger.kernel.org, xfs@oss.sgi.com, Spelic On Tue, Jun 19 2012 at 3:58pm -0400, Ted Ts'o wrote: > 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? The commit I referenced basically provides that capability. > 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). Documentation/device-mapper/thin-provisioning.txt has details on how to use dmsetup to create a thin device that uses a read-only external origin volume (so all reads to unprovisioned areas of the thin device will be remapped to the external origin -- "external" meaning the volume outside of the thin-pool). The creation of a thin device w/ a read-only external origin gets you started with a thin device that is effectively a snapshot of the origin volume. That thin device is read-write -- all writes are provisioned from the thin-pool that is backing the thin device. And you can take snapshots (or recursive snapshots) of that thin device. _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs