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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 57A46C76190 for ; Thu, 25 Jul 2019 19:14:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C2BF214AE for ; Thu, 25 Jul 2019 19:14:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="nQkukiVY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726621AbfGYTOK (ORCPT ); Thu, 25 Jul 2019 15:14:10 -0400 Received: from mail-io1-f65.google.com ([209.85.166.65]:45825 "EHLO mail-io1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726065AbfGYTOJ (ORCPT ); Thu, 25 Jul 2019 15:14:09 -0400 Received: by mail-io1-f65.google.com with SMTP id g20so99560759ioc.12 for ; Thu, 25 Jul 2019 12:14:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=wjSg/Tvpdr9T7FSXNKzBYEPcpgnCVbfs2X2a5aK2Wk8=; b=nQkukiVYE/FtTg3112qHNGfi787jdUaVPEr03VLWPXuS3gVK+cwfD5ig6NU2Pu4PjH wt3wOSavgcbEegYReD5mlHtEMJsBrzsfum0un8C9ZMeHKSaGSdoDaimOfetBBm+fF7k5 y7xGsob9iSVNS0AkTxuVNtTr80W54XjNa+9b4o+yMNnTJxjbSaXiYc1pCkgSBtArMqml W1FM6A58Sa+cfpT47gtUSNxHh9aiD1VSYjrpIj6nvMtn0O5XYoVGXEAoGNA5USM76gtw CABMMwVxFLbnbeWGtSgWWs3TbV4V3oJ1rfF6ZI7m8IO6vos30zIA5lAnhkQbZB0BM4mb xmDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=wjSg/Tvpdr9T7FSXNKzBYEPcpgnCVbfs2X2a5aK2Wk8=; b=GuGGIFICg/7IzrDkfHo5L6RWgk8ttsm+y7ZMSqjgftR2qtUvd/JnoI4nlTlS6lB1yI ENXj8s96rMkTVey4/6wZGZ5fLJPJv6NM4V0AIMcDg2Qb09If75KK3dSbnG7hmWhqAI37 O/dalvu5RYYogbcWxVSpaMPJYWsRrpD7zI1Rcn6A2Vmyr3lPOBx9AhW8NKJrtj2Fbyyj OTybP7LukqlTtp1bZqsrV98SDPwvq/oEEzP8PKRC9Fkzk7vPHPKNT7Ls9wAHtaCCN0iZ pXArNI1Pe30pavUW77VLO2fegonuyVIH+S+sGei6/UnPP4G7PGsNgDTQ1RHyAZy1XPES Li5w== X-Gm-Message-State: APjAAAVIohGIrc/LIxq980ptbI4ZP0oY03jVp8tYobKvTa+YoAvxZCoS 8aR8uBF7chaR8QNw0oASC0nnke/cZWQ= X-Google-Smtp-Source: APXvYqw0rFSAR/620Kr89jT18htWTkMpawBv4vOWpsrD9vc0cvdHo12lwgrqLsIsTdO/pwtDsKHsOA== X-Received: by 2002:a6b:d809:: with SMTP id y9mr86428267iob.301.1564082048525; Thu, 25 Jul 2019 12:14:08 -0700 (PDT) Received: from [191.9.209.46] (rrcs-70-62-41-24.central.biz.rr.com. [70.62.41.24]) by smtp.gmail.com with ESMTPSA id s3sm41864596iob.49.2019.07.25.12.14.07 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Jul 2019 12:14:08 -0700 (PDT) Subject: Re: [PATCH] btrfs: Allow more disks missing for RAID10 To: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org References: <20190718062749.11276-1-wqu@suse.com> <20190725183741.GX2868@twin.jikos.cz> From: "Austin S. Hemmelgarn" Message-ID: Date: Thu, 25 Jul 2019 15:14:05 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190725183741.GX2868@twin.jikos.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2019-07-25 14:37, David Sterba wrote: > On Thu, Jul 18, 2019 at 02:27:49PM +0800, Qu Wenruo wrote: >> RAID10 can accept as much as half of its disks to be missing, as long as >> each sub stripe still has a good mirror. > > Can you please make a test case for that? > > I think the number of devices that can be lost can be higher than a half > in some extreme cases: one device has copies of all stripes, 2nd copy > can be scattered randomly on the other devices, but that's highly > unlikely to happen. It is possible, but as you mention highly unlikely. It's also possible with raid1 mode too, and a lot less unlikely there (in fact, it's almost guaranteed to happen in certain configurations). > > On average it's same as raid1, but the more exact check can potentially > utilize the stripe layout. >