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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D258FC433EF for ; Sun, 9 Jan 2022 10:04:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235272AbiAIKEN (ORCPT ); Sun, 9 Jan 2022 05:04:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50740 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235266AbiAIKEN (ORCPT ); Sun, 9 Jan 2022 05:04:13 -0500 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4646EC06173F; Sun, 9 Jan 2022 02:04:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=RLHFLTnlH8sDPn3r0xOhlRONJ1BiiMvPu3kceWlRu9k=; b=mCNiyC3soTFC46BFeDvCah655q XOFlft46ytCVFNVrp+CxyxT96fEeQ9aRYtvwKz6JvGyJvvLY1T83Z1y0T0pxY5kXi0aOz2Fqu/Y/A /Gqxnx8oum1fYnufHU8Q2H7jpZvmPLvRuoY1GAMAihMGEE1MyRPutHV8UxG7gk62pxFEjW66EgOIg W0NPc2L79J+9QE6kTzjuInmqH6iHlCjkM5wyoPeoO8qmIdBbFovkfgnI0KqXwgNOl2NFhKSmga7uP 52zazEvLOm9i7sHoNqtOR4MDeuk1enahQQ3g3boWUTg9JEnCrw0KI9T7rAbcsD6nByjyfr7mSdKKW AzDjK2Qg==; Received: from [2001:8b0:10b:1:4a2a:e3ff:fe14:8625] (helo=u3832b3a9db3152.ant.amazon.com) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1n6V3X-007bqt-D4; Sun, 09 Jan 2022 10:04:07 +0000 Message-ID: Subject: Re: [dm-devel] Proper way to test RAID456? From: David Woodhouse To: Qu Wenruo , Lukas Straub Cc: Linux FS Devel , "linux-block@vger.kernel.org" , "dm-devel@redhat.com" , linux-raid@vger.kernel.org Date: Sun, 09 Jan 2022 10:04:05 +0000 In-Reply-To: <5ffc44f1-7e82-bc85-fbb1-a4f89711ae8f@gmx.com> References: <0535d6c3-dec3-fb49-3707-709e8d26b538@gmx.com> <20220108195259.33e9bdf0@gecko> <20220108202922.6b00de19@gecko> <5ffc44f1-7e82-bc85-fbb1-a4f89711ae8f@gmx.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-0zNPaCF1kEDLKbOWMWmq" User-Agent: Evolution 3.36.5-0ubuntu1 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org --=-0zNPaCF1kEDLKbOWMWmq Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2022-01-09 at 07:55 +0800, Qu Wenruo wrote: > On 2022/1/9 04:29, Lukas Straub wrote: > > But there is a even simpler solution for btrfs: It could just not touch > > stripes that already contain data. >=20 > That would waste a lot of space, if the fs is fragemented. >=20 > Or we have to write into data stripes when free space is low. >=20 > That's why I'm trying to implement a PPL-like journal for btrfs RAID56. PPL writes the P/Q of the unmodified chunks from the stripe, doesn't it? An alternative in a true file system which can do its own block allocation is to just calculate the P/Q of the final stripe after it's been modified, and write those (and) the updated data out to newly- allocated blocks instead of overwriting the original. Then the final step is to free the original data blocks and P/Q. This means that your RAID stripes no longer have a fixed topology; you need metadata to be able to *find* the component data and P/Q chunks... it ends up being non-trivial, but it has attractive properties if we can work it out. --=-0zNPaCF1kEDLKbOWMWmq Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEkQw ggYQMIID+KADAgECAhBNlCwQ1DvglAnFgS06KwZPMA0GCSqGSIb3DQEBDAUAMIGIMQswCQYDVQQG EwJVUzETMBEGA1UECBMKTmV3IEplcnNleTEUMBIGA1UEBxMLSmVyc2V5IENpdHkxHjAcBgNVBAoT FVRoZSBVU0VSVFJVU1QgTmV0d29yazEuMCwGA1UEAxMlVVNFUlRydXN0IFJTQSBDZXJ0aWZpY2F0 aW9uIEF1dGhvcml0eTAeFw0xODExMDIwMDAwMDBaFw0zMDEyMzEyMzU5NTlaMIGWMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRgwFgYD VQQKEw9TZWN0aWdvIExpbWl0ZWQxPjA8BgNVBAMTNVNlY3RpZ28gUlNBIENsaWVudCBBdXRoZW50 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