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=-2.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, 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 91558C432C0 for ; Thu, 28 Nov 2019 12:32:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5A41E21787 for ; Thu, 28 Nov 2019 12:32:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=gmx.net header.i=@gmx.net header.b="Z6Jfy8Sc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726565AbfK1Mco (ORCPT ); Thu, 28 Nov 2019 07:32:44 -0500 Received: from mout.gmx.net ([212.227.17.21]:44057 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726227AbfK1Mco (ORCPT ); Thu, 28 Nov 2019 07:32:44 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1574944163; bh=8oTIO1HXRvjdBEoNczZShr7X+1n3VkiuZQeiHR8pq1o=; h=X-UI-Sender-Class:Subject:To:References:From:Date:In-Reply-To; b=Z6Jfy8ScR3wrpgoUTLtUS5SpGbOQCoevsAzG3+s+WEf+ijOQVABI7s1hozd7nrJyf KJIhSVwsojtUkEGlbSt1IRllp/Q4QGsAUD/+BfYy8Au4tEkh7iL/9HdcnOW/kwg47l EBQYTzW+I+kTvsf7fNvpVPCsLkUx9/ti6pz4IP7w= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from [0.0.0.0] ([13.231.109.76]) by mail.gmx.com (mrgmx104 [212.227.17.174]) with ESMTPSA (Nemesis) id 1N0X8u-1hduwo3O6O-00wXKy; Thu, 28 Nov 2019 13:29:23 +0100 Subject: Re: [PATCH 3/3] btrfs: volumes: Allocate degraded chunks if rw devices can't fullfil a chunk To: dsterba@suse.cz, Anand Jain , Qu Wenruo , linux-btrfs@vger.kernel.org References: <20191107062710.67964-1-wqu@suse.com> <20191107062710.67964-4-wqu@suse.com> <6cc25dbd-55e4-43bb-7b95-86c62bee27c7@oracle.com> <20191127192329.GA2734@twin.jikos.cz> <8c0a2816-1a7d-7d75-f591-c8712a85efd5@gmx.com> <20191128112449.GF2734@twin.jikos.cz> From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; prefer-encrypt=mutual; keydata= mQENBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAG0IlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT6JAU4EEwEIADgCGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCXZw1oQAKCRDC PZHzoSX+qCY6CACd+mWu3okGwRKXju6bou+7VkqCaHTdyXwWFTsr+/0ly5nUdDtT3yEVggPJ 3VP70wjlrxUjNjFb6iIvGYxiPOrop1NGwGYvQktgRhaIhALG6rPoSSAhGNjwGVRw0km0PlIN D29BTj/lYEk+jVM1YL0QLgAE1AI3krihg/lp/fQT53wLhR8YZIF8ETXbClQG1vJ0cllPuEEv efKxRyiTSjB+PsozSvYWhXsPeJ+KKjFen7ebE5reQTPFzSHctCdPnoR/4jSPlnTlnEvLeqcD ZTuKfQe1gWrPeevQzgCtgBF/WjIOeJs41klnYzC3DymuQlmFubss0jShLOW8eSOOWhLRuQEN BFnVga8BCACqU+th4Esy/c8BnvliFAjAfpzhI1wH76FD1MJPmAhA3DnX5JDORcgaCbPEwhLj 1xlwTgpeT+QfDmGJ5B5BlrrQFZVE1fChEjiJvyiSAO4yQPkrPVYTI7Xj34FnscPj/IrRUUka 68MlHxPtFnAHr25VIuOS41lmYKYNwPNLRz9Ik6DmeTG3WJO2BQRNvXA0pXrJH1fNGSsRb+pK EKHKtL1803x71zQxCwLh+zLP1iXHVM5j8gX9zqupigQR/Cel2XPS44zWcDW8r7B0q1eW4Jrv 0x19p4P923voqn+joIAostyNTUjCeSrUdKth9jcdlam9X2DziA/DHDFfS5eq4fEvABEBAAGJ ATwEGAEIACYCGwwWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCXZw1rgUJCWpOfwAKCRDCPZHz oSX+qFcEB/95cs8cM1OQdE/GgOfCGxwgckMeWyzOR7bkAWW0lDVp2hpgJuxBW/gyfmtBnUai fnggx3EE3ev8HTysZU9q0h+TJwwJKGv6sUc8qcTGFDtavnnl+r6xDUY7A6GvXEsSoCEEynby 72byGeSovfq/4AWGNPBG1L61Exl+gbqfvbECP3ziXnob009+z9I4qXodHSYINfAkZkA523JG ap12LndJeLk3gfWNZfXEWyGnuciRGbqESkhIRav8ootsCIops/SqXm0/k+Kcl4gGUO/iD/T5 oagaDh0QtOd8RWSMwLxwn8uIhpH84Q4X1LadJ5NCgGa6xPP5qqRuiC+9gZqbq4Nj Message-ID: <4cec03f9-513d-9b77-5967-93d7bddf55ba@gmx.com> Date: Thu, 28 Nov 2019 20:29:18 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20191128112449.GF2734@twin.jikos.cz> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="C7VZumAk9GXcinqWkktluUSdKKT9MRGSu" X-Provags-ID: V03:K1:okKjoLHugC/1BMF/KoIwA/nmW/wqrVy5nWu91iCi3hT4qlaDV3N qK81mtlMBCAy6XVYRGaS8xttt00aV2OMvh8fT/eiRV24tBG4b/ygRoIbGOuo8HLnLz1IWql XR37uw16TEi+aaUUG/nWH7NFmxJHQx1yHxRh1r1Qe9hKMNMbfuN0dY6bFdYROEFatzM6eiL hwiK9MrHU8eJAiP9nxvkA== X-UI-Out-Filterresults: notjunk:1;V03:K0:rsICzGvlzI8=:JbUl6wD561UOmmMl8tqUdw LTFIIvTCLmv2V4sdngBo/rXm732kJpJ3HyeP29Wu9bRyFvNTGHiNWZs1BpOrR+h7KSkqin66l zJL9psNxW/uiVoXETVdpku4Ig5IQdMO496q/efpgyC/r/jLmbLlYHJL8ecRV57okbsEsHrY4A FfF4SDsJVnx3FkN5iFyJ5JdZhYpFG0pVNqQgtaTHe3HjPt4vgzpUocefH4IoFH1PNYdJklREc M6Pn+bVMsyx8LiGt+zAXC9NKlnv/fRKdH38c9upUHNvROQ1wboxdKKkgrmFdjp7qhEjJnOlS8 7H88FgFi9qIv2WeAFk/wbFX4aScUBz1NwNNUEIllctHNchYPYUj/LAU0183+UOhtmK72i4wqk LLHRDgDNPt/ZjLMLXNHqNlRqax9OE/RvKbqS5gzNjSFRsRd8/ctO8PIIYq5St6hKhAt3TPO/n Mduw+D784MqOts4fd11roYqbzc/5LsDZsILl6W6yVBbyngIVlXTibYKKdxX9XcKkot+KjUMWG XFJ2BUuktmejC/gcgBOpPiv/op2YmpCyrZVqWxC4twnycwH863yuLqYSfZXRZTPmen5XfH+fr obHKlmIdBjqL4tO5IJq1d0eQSlEnbwR8CmWZtI0oMVfpRSTTE+H18OAwzhgHCFmYmB00PELjH rhTXRn333fKGo0PQzMD7GYrFetajXBxdIofmgJ2qeoypHe49FWEcqQAAHumOHQ9J0fG7Wxk9H rV1Fkip9mwd2akB3nTHACUBomqvAoRQIXHXRrEijkpOugmcVDXD/vELVWWChS8PhCuqRCRnFq 1hDyezGxGi5MRl1NZGbnDCvSW/hk1RIbHks6Dupoz89UAeF17B1nPfibxmvDGo2EewL2lb7Ci iGm/FZHLfFtwM9wLHGMrxDKR/OKKlOYA+N3gi1OZRQsPpqjgAuYsOvu3NRDztRxk1z3+5kWsm yQnNXCnuaSnNDRfLvc1vko7Uj+8KpuZe20HTV6QRbqbAqiMrRZ4GPHItpDNTsFuWLTzNaFGO4 CAHtxCLeIZV+xFwm3dbZW1KtsfkLphFrFd0ch1fRX8z2bxniouG+TX7Vcf2NOyZyKXD2k/vAY D42NbwgcMw7fES4f6ajvkQOOS6tFscsy0r4betmRirq+dGYZnlx8jHOufN38TSa01enmY0DfP g+QaccJGKJTe4hxYeRMCd4gec1GdRWcpQ/1bN01ub5LM7ClxhGqR54WQUmn+AgnbC1ja86Sbj nSKWPLU3Ys5ic0CFK2mD5ScOQ2MMSxdtEVdsLGqLWoFjXRMUWinpOtiD8SgE= Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --C7VZumAk9GXcinqWkktluUSdKKT9MRGSu Content-Type: multipart/mixed; boundary="B8SNqhDtMC07sihyfMXs2mVH0w2LclKpV" --B8SNqhDtMC07sihyfMXs2mVH0w2LclKpV Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 2019/11/28 =E4=B8=8B=E5=8D=887:24, David Sterba wrote: > On Thu, Nov 28, 2019 at 07:36:41AM +0800, Qu Wenruo wrote: >> On 2019/11/28 =E4=B8=8A=E5=8D=883:23, David Sterba wrote: >>> On Tue, Nov 19, 2019 at 06:41:49PM +0800, Qu Wenruo wrote: >>>> On 2019/11/19 =E4=B8=8B=E5=8D=886:05, Anand Jain wrote: >>>>> On 11/7/19 2:27 PM, Qu Wenruo wrote: >>>>>> [PROBLEM] >>>>>> Btrfs degraded mount will fallback to SINGLE profile if there are = not >>>>>> enough devices: >>>>> >>>>> =C2=A0Its better to keep it like this for now until there is a fix = for the >>>>> =C2=A0write hole. Otherwise hitting the write hole bug in case of d= egraded >>>>> =C2=A0raid1 will be more prevalent. >>>> >>>> Write hole should be a problem for RAID5/6, not the degraded chunk >>>> feature itself. >>>> >>>> Furthermore, this design will try to avoid allocating chunks using >>>> missing devices. >>>> So even for 3 devices RAID5, new chunks will be allocated by using >>>> existing devices (2 devices RAID5), so no new write hole is introduc= ed. >>> >>> That this would allow a 2 device raid5 (from expected 3) is similar t= o >>> the reduced chunks, but now hidden because we don't have a detailed >>> report for stripes on devices. And rebalance would be needed to make >>> sure that's the filesystem is again 3 devices (and 1 device lost >>> tolerant). >>> >>> This is different to the 1 device missing for raid1, where scrub can >>> fix that (expected), but the balance is IMHO not. >>> >>> I'd suggest to allow allocation from missing devices only from the >>> profiles with redundancy. For now. >> >> But RAID5 itself supports 2 devices, right? >> And even 2 devices RAID5 can still tolerant 1 missing device. >=20 >> The tolerance hasn't changed in that case, just unbalanced disk usage = then. >=20 > Ah right, the constraints are still fine. That the usage is unbalanced > is something I'd still consider a problem because it's silently changin= g > the layout from the one that was set by user. Then it's the trade off between: - Completely the same layout - Just tolerance I'd say, even without missing device, btrfs by its nature, it can't ensure all chunks are allocated using the same device layout. E.g. 4 disk raid5, 1T + 2T + 2T + 2T. There will be a point where btrfs can only go 3 disks RAID5 other than 4.= >=20 > As there are two conflicting ways to continue from the missing device s= tate: >=20 > - try to use remaining devices to allow writes but change the layout > - don't allow writes, let user/admin sort it out >=20 > I'd rather have more time to understand the implications and try to > experiment with that. Sure, no problem. Thanks, Qu --B8SNqhDtMC07sihyfMXs2mVH0w2LclKpV-- --C7VZumAk9GXcinqWkktluUSdKKT9MRGSu Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEELd9y5aWlW6idqkLhwj2R86El/qgFAl3fvZ4ACgkQwj2R86El /qhlLwf/TEzEDZiXKNONO+LzMzXLEiQmPFzX5S52Im5PWJyQwcsom1GsL+UtiT5Y qNa2Hlozw/duK/XC3W3S+ds61fpzaxQvg4eiKMwj7OICh7iVkuJepAF22qf3sD9M 5k14LsE903SX8o0LMDBD59Z/BCPlpkrBkHhSIr+FXj+rleTFcV4V51f9PpfUJIp6 s/vmvxdHAOL8voLNUB+az5f7qptzEisVYEDcFhy7SB59cJIo4EtlFcBqHXYjpELA v7rMnfHpOaYhtZdUaXfxK0E1Lg8V9ojhkimIbzuJx/eSgWLM1f2DC642NH5jXQ9J HTHHbx13mpvTgu3abntAkhrTnBKpJw== =K4qA -----END PGP SIGNATURE----- --C7VZumAk9GXcinqWkktluUSdKKT9MRGSu--