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,URIBL_BLOCKED,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 2A062C432C0 for ; Thu, 28 Nov 2019 12:40:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E90A52084D for ; Thu, 28 Nov 2019 12:40:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=gmx.net header.i=@gmx.net header.b="aYvIuAZo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726609AbfK1Mky (ORCPT ); Thu, 28 Nov 2019 07:40:54 -0500 Received: from mout.gmx.net ([212.227.17.22]:55475 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726227AbfK1Mky (ORCPT ); Thu, 28 Nov 2019 07:40:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1574944776; bh=SKCMaRH936zg97zI02QMPiRAQPGPng8JCMN2Jdah1rw=; h=X-UI-Sender-Class:Subject:To:References:From:Date:In-Reply-To; b=aYvIuAZolZORvTxxHDjNJLhGr0rmmaK1ftjUm7lHMjfcGHNjn8uCrBTqIOQi2muC3 0DGsoXTjnCuzeFaiVgKzjeD4u1AfjuiOsY+wNLMAioC3D41mLOz5lkUCFha8mEttEa p0NPw95FnDRlAmvmtjZ1Zro5H3QQjzhlN0Is1Rrc= 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 1MK3Rm-1iEnxB4ADW-00La9l; Thu, 28 Nov 2019 13:39:36 +0100 Subject: Re: [PATCH 3/3] btrfs: volumes: Allocate degraded chunks if rw devices can't fullfil a chunk To: Qu WenRuo , "dsterba@suse.cz" , Anand Jain , "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> <366d5a96-4670-5839-6bef-e8d3a77fd00b@suse.com> 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: <4eb3d18b-b938-c52d-8cc8-c21433c15183@gmx.com> Date: Thu, 28 Nov 2019 20:39:31 +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: <366d5a96-4670-5839-6bef-e8d3a77fd00b@suse.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="uJWQPLi11BvHrGijVpM4HWv785P6o4D71" X-Provags-ID: V03:K1:Jzw7In5czesBgnxpLXYzovjQ4fwWdc2H2hBbTqyNhBlr4apjLgs DJYXUDnwKqzo0DUUbqOIHOzpOI5UacWnbb9cyNlvcYI+5I6lRiAsqoUJKB+v8W1nFtxjg8A Cn3zdmQ3PqnbFUxbhp7tVVl9Q27/qYiW+U1+mNE5MJBb8P2V+VKtczdHlF6szHr20zMCaAB gLaecbVrXQonquK/fPaIQ== X-UI-Out-Filterresults: notjunk:1;V03:K0:xm8t3foxMkQ=:K/1JipKKS38Sg1uybPMzao CmtKozhAJr2xNedJbTcyjzyt+sUe/jU6h1RY+T1MifertcOAq1BDrMxiWi9lUY/j//t8GYZ1/ D/8QBJ/f6JWed6OsWZVqFkbtgsWvd8LwTUTBqNUHYBX1dL8S7OjI8uiMGkTp28otcNByQhBDh WwFb9vI1KpUQfyAhFOe+f9mMqzUgF1Rw0Mt1bOgsuuRBMwOVSYEHOBA9nhOb2EhnqgGBs5iwe DbSasfLJ+9xYeb/eEW1lYy8rMgEKoASruaofWo+lIBd1yygrlEqnudzLkxPn5Q+v/xrxf+Y1N Zv+BXzu/lHo07RD8TrqWGhBK8O8eNlGcgSL/StL+SdGt4j6YppiNgxDcrU54q1qDS3V3zySuE 1CBsisx1v1On8IgJRPADKtpsk5CY8oxbsu/vT/7oqlOmfocl1hnsaXdYIIPxRNYkioTNfP2Wq v2NufRX0HcEItFFTtt2tgNvNzvtKksc3hdX2KULGvxC5eFBlRaFLnFYxtNF2dotof5I8JUyB4 QJYXK7/rQQrL+0A8a42sZe2h+2aKOURFSCemc9hGbOyh2aSymKdjcbzXRVAmOYHV1euVyqDbd Jrj4Qc5R3fi82Vm/2A8iEHVFt4mmB9u7+PVJLHOrcGqmYnjkRTy0nRQQNlqMCY0MdFxiUj0TL kTILl96x1wBIh0j0iSqrOFlUQhTlaosGqATDeNBxjpjbFCapIiljUx/XBGf29gY/cgCzenub6 /dRdElAM7kispu6+sTJGEX0ao8zYZhHr33CZa2pgiZHmHvSTy4R7/V8PTLbmkjZ/VK5k32bE3 Vcz08aVClWvowo614j2Ey/e0fudiY43KMQTmHQZkblPSHP9D0oLafNRDy50w5UIPyktHMUcUM PWgOCCJ+VdQkCvJznmFCZ8uGOzS58H+5EuSNRV/+q9DQWkbm590Y6G05H3tT4KznuZoLpDy0W GsBp3DhKBLid4mjrP8Ur9IXUaqYdpCrYv7VPOVkGksoSpMUlUyxccBpPKWxHa0UN8s7XZsL6D YPn6vbc6iA84ORGDpk/zmxuMA2P7axeMXnHDGL8JrFKDdLEngk32ojxUWU7dJoa1J0WuVjOMb 8///dAxofPqqRd0iX3Ca/gbKbn5MjDxQCwlpSqJXDq2hfVxe8uA/+D0+66aSAoXO2J1AYBhOO sXtgGEVhDEtXT58HCWI1133i67j1YydAqDpfipawvG7ODwJU9NnhZdMcLwJkql3/WIGnjVDVE YeycelztpAk80dnP4AFm94piwj6jwpf8lAwzEm7hksLonPQlndO5a8mlXunM= 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) --uJWQPLi11BvHrGijVpM4HWv785P6o4D71 Content-Type: multipart/mixed; boundary="mfwFf28n43XKHGKDlL0gAP0JDVB2q9Xc8" --mfwFf28n43XKHGKDlL0gAP0JDVB2q9Xc8 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=888:30, Qu WenRuo wrote: >=20 >=20 > 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 = degraded >>>>>> =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 introdu= ced. >>>> >>>> That this would allow a 2 device raid5 (from expected 3) is similar = to >>>> 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. >> >>> The tolerance hasn't changed in that case, just unbalanced disk usage= then. >> >> Ah right, the constraints are still fine. That the usage is unbalanced= >> is something I'd still consider a problem because it's silently changi= ng >> the layout from the one that was set by user. >> >> As there are two conflicting ways to continue from the missing device = state: >> >> - try to use remaining devices to allow writes but change the layout >> - don't allow writes, let user/admin sort it out >> >> I'd rather have more time to understand the implications and try to >> experiment with that. >> > Ah, makes sense. >=20 > So no need for a new version. >=20 > Reviewed-by: Qu Wenruo >=20 > Thanks, > Qu >=20 Facepalm, that's for another thread.... Reviewing patch from myself, WTF.... --mfwFf28n43XKHGKDlL0gAP0JDVB2q9Xc8-- --uJWQPLi11BvHrGijVpM4HWv785P6o4D71 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEELd9y5aWlW6idqkLhwj2R86El/qgFAl3fwAMACgkQwj2R86El /qiPWQf/bDgLwDe1tQzltFv7emeMqoq0gpDW8sT+raY46rWd1DuP8oYw2Az7kfG6 A0955olAxHcVbhHhJ7LUHE+/fi+p25UlL5bPAFfbiuiAiPpEe3VtlbeBCsf2pwgM +3tr+wLm3rzEkuCg3kDZuZLjp7NYoxr0qa/4ov8wjvuY2y2pM4VEVYWmh6YMEuFy AEcJJgnKAlp6stTrUcwLdE5qqW385TUoRrRY5kLtq5V++xnjfa5iKKijA3sW04L/ XqRk1JOyLECVbISXd/WvaaTFBPTUZYyYoVR+OkzdCbWcSy1VhG9RIcBVb5CMoHzt H7Lpw1k1mpdUMUOH8B40J2GjdQWoUQ== =niz+ -----END PGP SIGNATURE----- --uJWQPLi11BvHrGijVpM4HWv785P6o4D71--