From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 13AFDC54FD0 for ; Mon, 27 Apr 2020 11:29:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EA634206A4 for ; Mon, 27 Apr 2020 11:29:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726831AbgD0L3t (ORCPT ); Mon, 27 Apr 2020 07:29:49 -0400 Received: from mail.nethype.de ([5.9.56.24]:46733 "EHLO mail.nethype.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726390AbgD0L3t (ORCPT ); Mon, 27 Apr 2020 07:29:49 -0400 Received: from [10.0.0.5] (helo=doom.schmorp.de) by mail.nethype.de with esmtp (Exim 4.92) (envelope-from ) id 1jT1xL-001J4k-Ab; Mon, 27 Apr 2020 11:29:47 +0000 Received: from [10.0.0.1] (helo=cerebro.laendle) by doom.schmorp.de with esmtp (Exim 4.92) (envelope-from ) id 1jT1xL-00060v-66; Mon, 27 Apr 2020 11:29:47 +0000 Received: from root by cerebro.laendle with local (Exim 4.92) (envelope-from ) id 1jT1xL-0001fh-5Z; Mon, 27 Apr 2020 13:29:47 +0200 Date: Mon, 27 Apr 2020 13:29:47 +0200 From: Marc Lehmann To: Hugo Mills , linux-btrfs@vger.kernel.org Subject: Re: questoin about Data=single on multi-device fs Message-ID: <20200427112946.GA3648@schmorp.de> References: <20200426100405.GA5270@schmorp.de> <20200426102547.GM32577@savella.carfax.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200426102547.GM32577@savella.carfax.org.uk> OpenPGP: id=904ad2f81fb16978e7536f726dea2ba30bc39eb6; url=http://pgp.schmorp.de/schmorp-pgpkey.txt; preference=signencrypt Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Sun, Apr 26, 2020 at 11:25:47AM +0100, Hugo Mills wrote: > > The reason I chose data=single was specifically to help in case of device > > loss at the cost of performance. > > Make backups. That's the only way to be sure about this sort of thing. I think you are unthinkingly repeating a wrong (and slightly dangerous) claim - backups cannot actually do that sort of thing: a raid will protect against (some amount of) disk failures with no data loss, but backups cannot: Backups can protect against complete data loss, but cannot completely protect against data loss. > With single data, *chunk allocation* will go to the device with the > largest amount of unallocated space. If your data is WORM That is definitely not the case with 5.4 - I added two disks to an existing filesystem and copied 8TB onto it with btrfs receive, resulting in about 3800G used on both new disks, with Data=single. I repeated it by creating a 5 disk-fs and 1TB of data and got prettyx even distribution. -- The choice of a Deliantra, the free code+content MORPG -----==- _GNU_ http://www.deliantra.net ----==-- _ generation ---==---(_)__ __ ____ __ Marc Lehmann --==---/ / _ \/ // /\ \/ / schmorp@schmorp.de -=====/_/_//_/\_,_/ /_/\_\