From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from magic.merlins.org ([209.81.13.136]:42741 "EHLO mail1.merlins.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754345AbaEEFNl (ORCPT ); Mon, 5 May 2014 01:13:41 -0400 Date: Sun, 4 May 2014 22:06:17 -0700 From: Marc MERLIN To: Daniel Lee Cc: Brendan Hide , linux-btrfs@vger.kernel.org Subject: Re: Is metadata redundant over more than one drive with raid0 too? Message-ID: <20140505050617.GG10159@merlins.org> References: <20140503232702.GC9061@merlins.org> <5365E4CF.3050405@swiftspirit.co.za> <20140504072420.GJ9061@merlins.org> <5366DF48.40209@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <5366DF48.40209@gmail.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Sun, May 04, 2014 at 05:46:00PM -0700, Daniel Lee wrote: > This often seems to confuse people and I think there is a common > misconception that the btrfs raid/single/dup features work at the file > level when in reality they work at a level closer to lvm/md. > > If someone told you that they lost a device out of a jbod or multi disk > lvm group(somewhat analogous to -d single) with ext on top you would > expect them to lose data in any file that had a fragment in the lost > region (lets ignore metadata for a moment). This is potentially up to > 100% of the files but this should not be a surprising result. Similarly, > someone who has lost a disk out of a md/lvm raid0 volume should not be > surprised to have a hard time recovering any data at all from it. That's true, but in this case I barely see the point of -m single vs -m raid0. It sounds like they both stripe data anyway, maybe not at the same level, but if both are striped, than they're almost the same in my book :) Marc -- "A mouse is a device used to point at the xterm you want to type in" - A.S.R. Microsoft is to operating systems .... .... what McDonalds is to gourmet cooking Home page: http://marc.merlins.org/ | PGP 1024R/763BE901