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=-2.2 required=3.0 tests=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 E4851C7618B for ; Fri, 26 Jul 2019 10:38:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C274822BEF for ; Fri, 26 Jul 2019 10:38:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726489AbfGZKia (ORCPT ); Fri, 26 Jul 2019 06:38:30 -0400 Received: from mx2.suse.de ([195.135.220.15]:50848 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726000AbfGZKia (ORCPT ); Fri, 26 Jul 2019 06:38:30 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 9B8F3B629; Fri, 26 Jul 2019 10:38:28 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 7BF32DA80E; Fri, 26 Jul 2019 12:39:04 +0200 (CEST) Date: Fri, 26 Jul 2019 12:39:03 +0200 From: David Sterba To: Qu Wenruo Cc: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org Subject: Re: [PATCH] btrfs: Allow more disks missing for RAID10 Message-ID: <20190726103902.GZ2868@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Qu Wenruo , Qu Wenruo , linux-btrfs@vger.kernel.org References: <20190718062749.11276-1-wqu@suse.com> <20190725183741.GX2868@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Jul 26, 2019 at 07:41:41AM +0800, Qu Wenruo wrote: > > > On 2019/7/26 上午2:37, 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? > > Fstests one or btrfs-progs one? For fstests. > > 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. > > > > On average it's same as raid1, but the more exact check can potentially > > utilize the stripe layout. > > > That will be at extent level, to me it's an internal level violation, > far from what we want to improve. Ah I don't mean to go the extent level, as you implemented it is enough and an improvement.