Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752705AbYLQV2k (ORCPT ); Wed, 17 Dec 2008 16:28:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751737AbYLQV20 (ORCPT ); Wed, 17 Dec 2008 16:28:26 -0500 Received: from srv5.dvmed.net ([207.36.208.214]:58640 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751237AbYLQV2Z (ORCPT ); Wed, 17 Dec 2008 16:28:25 -0500 Message-ID: <49496EDE.5080101@garzik.org> Date: Wed, 17 Dec 2008 16:27:58 -0500 From: Jeff Garzik User-Agent: Thunderbird 2.0.0.18 (X11/20081119) MIME-Version: 1.0 To: Kay Sievers CC: Chris Mason , Andrew Morton , Christoph Hellwig , adilger@sun.com, sfr@canb.auug.org.au, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: Notes on support for multiple devices for a single filesystem References: <1227183484.6161.17.camel@think.oraclecorp.com> <1228962896.21376.11.camel@think.oraclecorp.com> <20081211141436.030c2d65.sfr@canb.auug.org.au> <20081210200604.8e190b0d.akpm@linux-foundation.org> <1229006596.22236.46.camel@think.oraclecorp.com> <20081215210323.GB5000@webber.adilger.int> <20081217132343.GA14695@infradead.org> <20081217115325.3312858a.akpm@linux-foundation.org> <1229547485.27170.77.camel@think.oraclecorp.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Kay Sievers wrote: > Features like the very nice and useful directory-based snapshots would > also not be possible with simple block-based multi-devices, right? Snapshotting via block device has always been an incredibly dumb hack, existing primarily because filesystem-based snapshots did not exist for the filesystem in question. Snapshots are better at the filesystem level because the filesystem is the only entity that knows when the filesystem is quiescent and snapshot-able. ISTR we had to add ->write_super_lockfs() to hack in support for LVM in this manner, rather than doing it the right way. Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/