From: Theodore Tso Subject: Re: [PATCH] blkid: optimize dm_device_is_leaf() usage Date: Tue, 26 Aug 2008 16:00:28 -0400 Message-ID: <20080826200028.GA29936@mit.edu> References: <1219697316-5632-1-git-send-email-kzak@redhat.com> <20080826122405.GA8720@mit.edu> <20080826135102.GK6029@nb.net.home> <20080826144721.GD8720@mit.edu> <20080826194445.GN3392@webber.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Karel Zak , linux-ext4@vger.kernel.org, Eric Sandeen , mbroz@redhat.com, agk@redhat.com To: Andreas Dilger Return-path: Received: from www.church-of-our-saviour.org ([69.25.196.31]:39757 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753869AbYHZUAb (ORCPT ); Tue, 26 Aug 2008 16:00:31 -0400 Content-Disposition: inline In-Reply-To: <20080826194445.GN3392@webber.adilger.int> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Aug 26, 2008 at 01:44:45PM -0600, Andreas Dilger wrote: > On Aug 26, 2008 10:47 -0400, Theodore Ts'o wrote: > > I don't think you mean multipath support in terms of where there are > > multiple paths to the same physical device ala fiber channel, but > > rather where are multiple devices which are built on each other, > > right? So where /dev/sda is used to create the LVM PV's, and so on, > > right? > > No, in fact DM has actual mutliple-paths-to-the-same-device support, > via "dm-multipath". Well, *that* we have, as long as the parent devices are real (non-devicemapper) devices. So if /dev/sdc and /dev/sdg are both paths to the same filesystem, and dm-multipath has created /dev/mapper/filesystem as the multipath device to that filesystem, any devices with /dev/mapper have priority over non-dm devices, so /dev/mapper/filesystem will get returned first. - Ted