From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailgw-01.dd24.net ([193.46.215.41]:33352 "EHLO mailgw-01.dd24.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932768AbcIXSJd (ORCPT ); Sat, 24 Sep 2016 14:09:33 -0400 Received: from mailpolicy-01.live.igb.homer.key-systems.net (mailpolicy-01.live.igb.homer.key-systems.net [192.168.1.26]) by mailgw-01.dd24.net (Postfix) with ESMTP id 9FC665FE51 for ; Sat, 24 Sep 2016 18:09:30 +0000 (UTC) Received: from mailgw-01.dd24.net ([192.168.1.35]) by mailpolicy-01.live.igb.homer.key-systems.net (mailpolicy-01.live.igb.homer.key-systems.net [192.168.1.25]) (amavisd-new, port 10235) with ESMTP id AME7IpOlvAz0 for ; Sat, 24 Sep 2016 18:09:28 +0000 (UTC) Received: from [192.168.177.212] (51.red-81-38-116.dynamicip.rima-tde.net [81.38.116.51]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mailgw-01.dd24.net (Postfix) with ESMTPSA for ; Sat, 24 Sep 2016 18:09:27 +0000 (UTC) Message-ID: <1474740566.7196.4.camel@scientia.net> Subject: Re: Does data checksumming remain for files with No_COW file attribute? From: Christoph Anton Mitterer To: linux-btrfs@vger.kernel.org Date: Sat, 24 Sep 2016 20:09:26 +0200 In-Reply-To: <20160924174012.51d44caa@natsu> References: <767591474719974@web21o.yandex.ru> <20160924174012.51d44caa@natsu> Content-Type: multipart/signed; micalg="sha-512"; protocol="application/x-pkcs7-signature"; boundary="=-sIVMJHg49QFs7E7Z/o0d" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: --=-sIVMJHg49QFs7E7Z/o0d Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sat, 2016-09-24 at 17:40 +0500, Roman Mamedov wrote: > Yes. IIRC the reasoning was that it's more difficult to track > checksums of > data which is being overwritten in-place (as opposed to CoW). AFAIU it wouldn't be more difficult, since the meta-data itself is still subject to CoW... There's just no guarantee in the case of a crash, that checksum and data match (which is IMO however a small price to pay - especially as the data is in that case and without CoW anyway not guaranteed to be valid - compared to all sorts of other silent corruptions against which checksums protect... not to talk about the ability to actually repair files in case of RAID inconsistencies. > You can't apply chattr +C to any files of non-zero length, so by > definition > there won't be any pre-existing checksummed extents in that file. Speaking of which,... can't one modify chattr properly so that it gives an error message and $? !=3D 0 in that case? 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