Comments on: More Filesystem Foo

By: Danyel Lawson

Danyel Lawson — Fri, 09 May 2008 18:38:38 +0000

For reiserfs you may want to make sure you haven’t enabled notall in the mount options. Tailing allows reiserfs to use variable block sizes. Filling in the gaps between large files using big block sizes.

By: textshell

textshell — Fri, 25 Apr 2008 15:24:36 +0000

I think your test is not very good. Some filesystems reserve space for metadata at file system creation and count it all as used and some filesystems account for the metadata only if it’s used.
So if you want to test how good they manage space add files to the FS (as root to avoid 5% for root reserves and such things) with realistic average size (or size distribution) until you get no space left on device and compare the total size of all saved files. (using du without accounting for filesystem overhead)

By: Sacha

Sacha — Thu, 24 Apr 2008 23:31:50 +0000

You do realise that the data you entered using ‘dd’ took exactly the same space on each filesystem right? So what was the compare?

The only reason some filesystems have less used than others is because of the 5% reserved for root on ext2/ext3 and reiser filesystem. You can disable this using -m 0 when creating or tuning.

You attempted to compare but somehow your conclusion is that all filesystems are equal. Try enabling most compression possible on each filesystem (since you don’t care about speed) and don’t use ‘dd’ to add data. Try pasting the linux kernel source on to there or something.

You’ll find that reiser fs wins in such a benchmark (I have seen many of these before). It has a better compression.

By: hk47

hk47 — Thu, 24 Apr 2008 12:01:43 +0000

Try:
$ tune2fs -m 0 /dev/mapper/test-ext2

That should give you roughly the same amount of free space on (a freshly created) ext2 as on vfat or xfs. Likewise for ext3 minus journal data.

You might be interested in reading this article, though it’s from 2006:
http://www.debian-administration.org/articles/388

By: Roger Binns

Roger Binns — Thu, 24 Apr 2008 09:36:43 +0000

Note that unix filesystems typically under report free space by 5% as that is reserved for root. In any event a better test is to create a directory structure with numerous small files such as untarring linux kernel source (directories can take up quite a bit of space) and then see what is the largest file you can create in the remaining space (dd if=/dev/urandom of=/mnt/$i/foo.img) – using /dev/zero allows the filesystem to create sparse files taking up no space hence using urandom.