From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753604AbZEZEqP (ORCPT ); Tue, 26 May 2009 00:46:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751925AbZEZEp7 (ORCPT ); Tue, 26 May 2009 00:45:59 -0400 Received: from faui03.informatik.uni-erlangen.de ([131.188.30.103]:58666 "EHLO faui03.informatik.uni-erlangen.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751626AbZEZEp6 (ORCPT ); Tue, 26 May 2009 00:45:58 -0400 Date: Tue, 26 May 2009 06:45:59 +0200 From: Thomas Glanzmann To: Bill Davidsen Cc: tytso@thunk.org, LKML , linux-ext4@vger.kernel.org Subject: Re: zero out blocks of freed user data for operation a virtual machine environment Message-ID: <20090526044559.GB10980@cip.informatik.uni-erlangen.de> Mail-Followup-To: Thomas Glanzmann , Bill Davidsen , tytso@thunk.org, LKML , linux-ext4@vger.kernel.org References: <20090524170045.GC24753@cip.informatik.uni-erlangen.de> <4A1B0B4A.8050706@tmr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A1B0B4A.8050706@tmr.com> User-Agent: Mutt/1.5.15 (2007-05-02) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Bill, I think you didn't read what I write so here is it again: My applications are VMs. Every disk that you give to a VM is zeroed out, one way ot the other: One way is to use dd or something that has the same effect the other is using a sparse file. That is guranteed. Now as soon as you start working in this VM it is not guranteed because on real live applications it makes limited sense to zero out freed blocks (expect maybe you have a SAN LUN exported from a storage device that supports data deduplication or if you want that deleted files disappear from you block device). Todays datadeduplication and backupsolutions for VM depend on the property that unused data blocks are zeroed out. And actually I can't think of an easier interface. As I proposed earlier, if you don't like it for performance reasons, that's fine, but if you have to backup 5.6 Terabyte instead of 17 Terabyte than this is a huge space safer even with the performance overhead involved. Thomas