From mboxrd@z Thu Jan 1 00:00:00 1970 From: mfe555 Subject: Re: Significant difference in 'file size' and 'disk usage' for single files Date: Sun, 5 Nov 2017 12:16:12 +0100 Message-ID: References: <472fde11-654a-4826-0256-46149e90216e@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: mfe555 To: linux-ext4@vger.kernel.org Return-path: Received: from mout.web.de ([212.227.15.4]:53422 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750725AbdKELQF (ORCPT ); Sun, 5 Nov 2017 06:16:05 -0500 In-Reply-To: <472fde11-654a-4826-0256-46149e90216e@web.de> Sender: linux-ext4-owner@vger.kernel.org List-ID: Some follow-up: The issue only occurs with "bigalloc" enabled. echo 3 > /proc/sys/vm/drop_caches seems to detach the blocked disk space from the files (so that 'du file' no longer includes the offset), but it does not free the space, 'df' still shows all file overheads as used disk space. Am 02.11.2017 um 20:17 schrieb mfe555: > Hi, I'm using ext4 on a Linux based Enigma2 set-top box, kernel 4.8.3. > > When creating a fresh file, there is a significant difference in file > size (ls -la) and disk usage (du). When making two copies of the file .. > > gbquad:/hdd/test# cp file file.copy1 > gbquad:/hdd/test# cp file file.copy2 > gbquad:/hdd/test# ls -la > -rw------- 1 root root 581821460 Nov 1 18:52 file > -rw------- 1 root root 581821460 Nov 1 18:56 file.copy1 > -rw------- 1 root root 581821460 Nov 1 18:57 file.copy2 > gbquad:/hdd/test# du * > 607232 file > 658176 file.copy1 > 644864 file.copy2 > > ... all three files show an overhead in the ~10% range, and the > overhead is different for these files although their md5sums are equal. > > When deleting a file (rm), the overhead remains occupied on the disk. > For example, after deleting "file", "df" reports approx. 581821460 > more bytes free, not 607232 kbytes more free space. The overhead > (607232 kB - 581821460 B =pprox. 39 MB) remains blocked. > > When re-booting, the blocked space becomes free again, and in addition > the overhead of those files that were not deleted also disappears, so > that after a reboot the'file size' and 'disk usage' match for all > files (except for rounding up to some block size). > > A colleague and I have observed this on two different "kernel 4.8.3" > boxes and three ext4 disks, but not on a "kernel 3.14" box also using > ext4. > > Can anyone help me with this ? > > Thanks a lot > Lukas >