From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maciej Marcin Piechotka Subject: Re: Inefficient storing of ISO images with compress=lzo Date: Tue, 20 Sep 2011 01:06:17 +0200 Message-ID: <1316473579.31049.2.camel@picard> References: <1316388769.2499.4.camel@picard> <4E76AEB9.4080109@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: linux-btrfs@vger.kernel.org To: Li Zefan Return-path: In-Reply-To: <4E76AEB9.4080109@cn.fujitsu.com> List-ID: On Mon, 2011-09-19 at 10:53 +0800, Li Zefan wrote: > Maciej Marcin Piechotka wrote: > > I've noticed that: > > > > - with x86-64 Fedora 15 DVD install images: > > - du -sh was 36 GB > > - btrfs df | grep -i data have shown over 40 GB used > > - without > > - du -sh is 34 GB > > - btrfs df | grep -i data have shown less then 34 GB used > > > > It seems that iso files are considered compressable while they may not be (and penalty is severe - 3x). > > > > With compress option specified, btrfs will try to compress the file, at most > 128K at one time, and if the compressed result is not smaller, the file will > be marked as uncompressable. > > I just tried with Fedora-14-i386-DVD.iso, and the first 896K is compressed, > with a compress ratio about 71.7%, and the remaining data is not compressed. > > -- > Li Zefan Just a question from person who don't know how btrfs operates - what if the beginning of file is well compressable and the rest is not? In any case the compression was my uneducated guess where is missing 4GB. Regards