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=-4.0 required=3.0 tests=BAYES_00, 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 355BEC433E0 for ; Fri, 31 Jul 2020 10:06:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16A33208E4 for ; Fri, 31 Jul 2020 10:06:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732279AbgGaKG3 (ORCPT ); Fri, 31 Jul 2020 06:06:29 -0400 Received: from dcvr.yhbt.net ([64.71.152.64]:38298 "EHLO dcvr.yhbt.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732140AbgGaKG3 (ORCPT ); Fri, 31 Jul 2020 06:06:29 -0400 Received: from localhost (dcvr.yhbt.net [127.0.0.1]) by dcvr.yhbt.net (Postfix) with ESMTP id C1E4A1F5AE; Fri, 31 Jul 2020 10:06:28 +0000 (UTC) Date: Fri, 31 Jul 2020 10:06:28 +0000 From: Eric Wong To: Alberto Bursi Cc: linux-btrfs@vger.kernel.org Subject: Re: raid1 with several old drives and a big new one Message-ID: <20200731100628.GA18568@dcvr> References: <20200731001652.GA28434@dcvr> <6d29319f-301e-c1d2-9674-b39619356ae7@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <6d29319f-301e-c1d2-9674-b39619356ae7@gmail.com> Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Alberto Bursi wrote: > On 31/07/20 02:16, Eric Wong wrote: > > Say I have three ancient 2TB HDDs and one new 6TB HDD, is there > > a way I can ensure one raid1 copy of the data stays on the new > > 6TB HDD? > > > > I expect the 2TB HDDs to fail sooner than the 6TB HDD given > > their age (>5 years). > > > > I'm not sure what is the problem, ok maybe the drives are old and are more > likely to fail, but why would more than one drive fail at once? Why wouldn't they? Otherwise there'd be no reason for RAID6 to exist over RAID5. Recovery puts more stress on the remaining drives and increases the likelyhood of another drive in a pool failing. I've seen HW RAID5 arrays lost like like this in a previous life (I didn't manage to convince the other sysadmins to use RAID6 :<).