From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ipmail06.adl2.internode.on.net ([150.101.137.129]:45988 "EHLO ipmail06.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752115AbeENW5z (ORCPT ); Mon, 14 May 2018 18:57:55 -0400 Date: Tue, 15 May 2018 08:57:51 +1000 From: Dave Chinner Subject: Re: How to reliably measure fs usage with reflinks enabled? Message-ID: <20180514225751.GB10363@dastard> References: <5398ddaf2b876c3563bc1c2927bfe1b9@ruhr-uni-bochum.de> <866a5e96-e900-d330-0efb-6413f85f86a3@sandeen.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <866a5e96-e900-d330-0efb-6413f85f86a3@sandeen.net> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Eric Sandeen Cc: Tarik Ceylan , linux-xfs@vger.kernel.org On Mon, May 14, 2018 at 05:02:53PM -0500, Eric Sandeen wrote: > > > On 5/14/18 3:02 PM, Tarik Ceylan wrote: > > How can one reliably measure filesystem usage on partitions that were compiled with -m reflink=1 ? > > Here are some numbers i am measuring with df -h (on different partitions holding the same data): > > 7.7G of 36G  (-b size=512  -m crc=0 ) > > 8.6G of 36G  (-b size=4096 -m crc=1 ) > > 8x larger inodes will take 8x more space, but you didn't say how many > inodes you have allocated. > > > 11G  of 36G  (-b size=1024 -m crc=1,reflink=1,rmapbt=1 -i sparse=1 ) > > 32G  of 864G (-b size=4096 -m crc=1,reflink=1 ) > > In that last case, you have a wildly different total fs size, so probably > no fair comparison here either. > > The reverse mapping btree also takes up space. You're turning too many > knobs at once. ;) Also, we reserve a lot of space for reflink/rmapbt metadata that isn't actually used, so you're not actually using any more space than the "-b size=4096 -m crc=1" case. I have plans for hiding that reservation from users so that we don't get questions like this.... Cheers, Dave. -- Dave Chinner david@fromorbit.com