Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751831Ab1FKFlm (ORCPT ); Sat, 11 Jun 2011 01:41:42 -0400 Received: from mail-ww0-f42.google.com ([74.125.82.42]:52693 "EHLO mail-ww0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750820Ab1FKFlj convert rfc822-to-8bit (ORCPT ); Sat, 11 Jun 2011 01:41:39 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=xCjc/QBtij6zscRUkM/i1L2YSzME/e2zcyHUNR0W0MGVoWXBr3bYtl4YLlHt1Xv0wa H2B1FGdIAGVkVaq8jJ24Sgm7QK01Am75q4fwt9xdkq6P/mbIMQenOAR564KqHN6qKTsh 1aB1+kpSfluCxi3fg/0ZpiSk6/pPjn7nu1NHg= MIME-Version: 1.0 In-Reply-To: <20110610101142.GA10144@ubuntu> References: <20110610101142.GA10144@ubuntu> Date: Sat, 11 Jun 2011 08:41:38 +0300 X-Google-Sender-Auth: 1utDBuhB5Q8qvxH0DC_NciZnM-Y Message-ID: Subject: Re: LVM vs. Ext4 snapshots (was: [PATCH v1 00/30] Ext4 snapshots) From: "Amir G." To: Joe Thornber Cc: Lukas Czerner , Mike Snitzer , linux-ext4@vger.kernel.org, tytso@mit.edu, linux-kernel@vger.kernel.org, lvm-devel@redhat.com, linux-fsdevel Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1917 Lines: 45 On Fri, Jun 10, 2011 at 1:11 PM, Joe Thornber wrote: > On Fri, Jun 10, 2011 at 11:01:41AM +0200, Lukas Czerner wrote: >> On Fri, 10 Jun 2011, Amir G. wrote: >> >> > CC'ing lvm-devel and fsdevel >> > >> > >> > On Wed, Jun 8, 2011 at 9:26 PM, Amir G. wrote: >> > For the sake of letting everyone understand the differences and trade >> > offs between >> > LVM and ext4 snapshots, so ext4 snapshots can get a fair trial, I need >> > to ask you >> > some questions about the implementation, which I could not figure out by myself >> > from reading the documents. > > First up let me say that I'm not intending to support writeable > _external_ origins with multisnap. ?This will come as a suprise to > many people, but I don't think we can resolve the dual requirements to > efficiently update many, many snapshots when a write occurs _and_ make > those snapshots quick to delete (when you're encouraging people to > take lots of snapshots performance of delete becomes a real issue). > If I understand this article correctly: http://people.redhat.com/mpatocka/papers/shared-snapshots.pdf It says that _external_ origin write updates can be efficient to readonly (or not written) snapshots. Could you not support readonly snapshots of an _external_ origin? You could even support writable snapshots, that will degrade write performance to origin temporarily. It can be useful, if one wants to "try-out" mounting a temporary writable snapshot, when the origin is not even mounted. After the "try-out", the temporary snapshot can be deleted and origin write performance would go back to normal. Is that correct? Amir. -- 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/