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=-3.8 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 E709BC433ED for ; Thu, 20 May 2021 20:49:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF8D961353 for ; Thu, 20 May 2021 20:49:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229578AbhETUuu (ORCPT ); Thu, 20 May 2021 16:50:50 -0400 Received: from icebox.esperi.org.uk ([81.187.191.129]:35976 "EHLO mail.esperi.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229519AbhETUuu (ORCPT ); Thu, 20 May 2021 16:50:50 -0400 Received: from loom (nix@sidle.srvr.nix [192.168.14.8]) by mail.esperi.org.uk (8.16.1/8.16.1) with ESMTPS id 14KKnQ1m025777 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Thu, 20 May 2021 21:49:26 +0100 From: Nix To: Leslie Rhorer Cc: antlists , Linux RAID Subject: Re: My superblocks have gone missing, can't reassemble raid5 References: <3f77fc62-2698-a8cb-f366-75e8a63b9a8b@att.net> <60A55239.9070009@youngman.org.uk> <8ab0ec19-4d9b-3de6-59cf-9e6a8a18bd37@att.net> <60de3096-95e8-ca32-3c83-982bf8409167@att.net> Emacs: don't cry -- it won't help. Date: Thu, 20 May 2021 21:49:26 +0100 In-Reply-To: <60de3096-95e8-ca32-3c83-982bf8409167@att.net> (Leslie Rhorer's message of "Wed, 19 May 2021 18:45:47 -0500") Message-ID: <87a6opnnah.fsf@esperi.org.uk> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-DCC-x.dcc-servers-Metrics: loom 104; Body=3 Fuz1=3 Fuz2=3 Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On 20 May 2021, Leslie Rhorer outgrape: > On 5/19/2021 3:01 PM, antlists wrote: >> Yes you can explicitly specify everything, and get mdadm to recover the array if the superblocks have been lost, but it's nowhere >> as simple as "there are only three possible combinations". > > The number of permutations of the order of three drives is precisely six. The permutations are: > > 1, 2, 3 > > 1, 3, 2 > > 2, 1, 3 > > 2, 3, 1 > > 3, 1, 2 > > 3, 2, 1 > > The Examine stated it was 2, 3, 1, but the device order is not > at all unlikely to have changed. Once again, I was very explicit in > saying the simple create may not work and if not he is facing some > much more serious issues. That was and is in no way incorrect. The > odds one of them will work are not terrible, and if so, he is in good > shape. Are you seriously implying there is no way any of them could > possibly work? Of course not, but it's *likely* none will work. mdadm's default chunk size has probably changed since the array was created if it's more than a few years old, for starters.