From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailgw-02.dd24.net ([193.46.215.43]:50583 "EHLO mailgw-02.dd24.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753074AbdHNMc4 (ORCPT ); Mon, 14 Aug 2017 08:32:56 -0400 Message-ID: <1502713969.3608.3.camel@scientia.net> Subject: Re: RedHat 7.4 Release Notes: "Btrfs has been deprecated" - wut? From: Christoph Anton Mitterer To: Qu Wenruo Cc: Btrfs BTRFS Date: Mon, 14 Aug 2017 14:32:49 +0200 In-Reply-To: References: <84806456-eed9-00b9-b3f6-99e46cefba33@swiftspirit.co.za> <4c094049-f8c8-a0ea-674b-33c6905d744a@gmx.com> <1502496618.6092.6.camel@scientia.net> <20170812074248.GA3352@infradead.org> Content-Type: multipart/signed; micalg="sha-512"; protocol="application/x-pkcs7-signature"; boundary="=-Wt9eUz2xK2cedPtcZvDY" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: --=-Wt9eUz2xK2cedPtcZvDY Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2017-08-14 at 15:46 +0800, Qu Wenruo wrote: > The problem here is, if you enable csum and even data is updated=C2=A0 > correctly, only metadata is trashed, then you can't even read out > the=C2=A0 > correct data. So what? This problem occurs anyway *only* in case of a crash,.. and *only* if notdatacow+checksumung would be used. A case in which currently, the user can either only hope that his data is fine (unless higher levels provide some checksumming means[0]), or anyway needs to recover from a backup. Intuitively I'd also say it's much less likely that the data (which is more in terms of space) is written correctly while the checksum is not. Or is it? [0] And when I've investigated back when discussion rose up the first time and some list member claimed that most typical cases (DBs, VM images) would anyway do their own checksuming,... I came to the conclusion that most did not even support it and even if they would it's no enabled per default and not really a *full* checksumming in most cases. > As btrfs csum checker will just prevent you from reading out any > data=C2=A0 > which doesn't match with csum. As I've said before, a tool could be provided, that re-computes the checksums then (making the data accessible again)... or one could simply mount the fs with nochecksum or some other special option, which allows bypassing any checks. > Now it's not just data corruption, but data loss then. I think the former is worse than the later. The later gives you a chance of noting it, and either recover from a backup, regenerate the data (if possible) or manually mark the data as being "good" (though corrupted) again. Cheers, Chris. --=-Wt9eUz2xK2cedPtcZvDY Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCCEmow ggXiMIIDyqADAgECAhBctkhuRwyYxn/2gNtkSuKNMA0GCSqGSIb3DQEBCwUAMH0xCzAJBgNVBAYT AklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSswKQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0 aWZpY2F0ZSBTaWduaW5nMSkwJwYDVQQDEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0 eTAeFw0xNTEyMTYwMTAwMDVaFw0zMDEyMTYwMTAwMDVaMHUxCzAJBgNVBAYTAklMMRYwFAYDVQQK Ew1TdGFydENvbSBMdGQuMSkwJwYDVQQLEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0 eTEjMCEGA1UEAxMaU3RhcnRDb20gQ2xhc3MgMiBDbGllbnQgQ0EwggEiMA0GCSqGSIb3DQEBAQUA A4IBDwAwggEKAoIBAQDuD1CMlQkjhKz1UGqP1jeiTiH9MgllRz6vOPrVG/eE0H/J4QQLV/PeL8RT 4xc44bEzsoJu0IhwnEchb+TxE/qw88w7hxODuw3N8Faxix6a1jp83+RWvZHZf78+O+3GYBpekZfT Oe9A/FoTXbcgwZfLTMQodn+ckNnX31M/1M2f2/7VA7QBlvihontyHQOlIlryQXnGI0UMCD21oopK 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