From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay5-d.mail.gandi.net ([217.70.183.197]:48493 "EHLO relay5-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752172AbaJ0NKq convert rfc822-to-8bit (ORCPT ); Mon, 27 Oct 2014 09:10:46 -0400 From: =?ISO-8859-1?Q?Sw=E2mi?= Petaramesh To: Marc Dietrich Cc: linux-btrfs@vger.kernel.org Subject: Re: nocow and compression Date: Mon, 27 Oct 2014 14:10:42 +0100 Message-ID: <1443833.UFNBsg354b@vajra> In-Reply-To: <2583846.rYj5NyAvhi@fb07-iapwap2> References: <2033879.2EPALEPetI@fb07-iapwap2> <2878318.cpxBgqOiao@vajra> <2583846.rYj5NyAvhi@fb07-iapwap2> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Sender: linux-btrfs-owner@vger.kernel.org List-ID: As far as I understood, "NOCOW" means that modified parts of files be rewritten into place, whereas compression causes compressed blocks of variable sizes to be created (depending upon their compression ratio). Changing a block in a file will most probably change its compressed size, and then you see why it cannot be rewritten into place... Somebody correct me if I'm wrong ;-) Le lundi 27 octobre 2014, 14:06:36 Marc Dietrich a écrit : > > > > « Compression does not work for NOCOW files » is clearly stated in > > > > https://btrfs.wiki.kernel.org/index.php/Compression#How_does_compression_i > > nt eract_with_direct_IO_or_COW.3F > > ah, sorry, I somehow overlooked this. > > Thanks > > Marc -- Swâmi Petaramesh http://petaramesh.org PGP 9076E32E Tout être manifesté est là pour embaumer, pour exprimer la Présence. -- Jean-Marc Mantel